AUTHOR’S EDITION. HISTOLOGY OF THE LOCUST (Calopteirus) AND OF THE CRICKET (Anabrus). BY CHABLES SEDGEWICK MINOT. [Extracted from the Second Report of the United States Entomological Commission.] 1880. AUTHOR’S EDITION". HISTOLOGY OF THE LOCTJST ( Caloptenns) AND OF THE CRICKET (Anabrus). BY \y CHARLES SEDGEWXCK MIXOT. [Extracted from the Second Report-of the United States Entomological Commission.] 18 8 0. CHAPTER X. HISTOLOGY OF THE LOCUST (CALOPTEXUS) AXD THE CRICKET (AXABRUS). (Plates II-VIII.) By Dr. Charles Sedgwick Minot. Insects have hitherto been but little studied by histologists. The science of general anatomy or histology, which was first established by Bichat in France, acquired a fresh importance and new meaning through the investigations of German naturalists, and above all through the great discovery of Schwann that all animals are composed, like plants, of certain minute elements or units, which are now familiar to all natu- 184 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. ralists under the name of cells. Cells are found only in living bodiesj and it is very probable, though by no means certain, that no life exists outside of cells, or in any other bodies. For this reason, to determine the essential powers and peculiarities of cells, and to discover the modi- fications they undergo, is the fundamental problem of zoology and botany at present. Indeed, biology might almost be defined as the science of cells. Since, however, microscopic anatomy, which is that branch of science which deals especially with the forms and appearance of cells, has been more actively prosecuted by medical men than by zoologists, our knowl- edge of the tissues of the higher vertebrates is much more complete than of the lower animals. Of the histological structure of insects singu- larly little is known, although they are particularly favorable objects for microscopic investigation. The most extensive series of observations are those of Leydig, which are summarized in part in his invaluable Lehrbuch der Histologic, published in 1858, and in part in shorter special papers scattered through various scientific journals of the last twenty years. Max Schultze has made several important contributions, and there are besides a few excellent single papers, by various authors, notably Dr. Yon Basch, Landois, Claparede, Graber, O. Schmidt, &c. Several of Professor Rudolph Leuekart’s pupils have made very valuable additions to our knowledge of insect histology. The writings of earlier naturalists contain many observations of importance, but the ground covered by them must now be gone over again and viewed from the stand-point of modern anatomy. When I began the work the results of which are here described in detail,223 1 found that very feflr histological observations had been made on the grasshoppers, or, indeed, on other insects. I feel that this is very unfortunate, because it prevents my judging of the accuracy of my own observations by comparing them with the results obtained by others. I must therefore anticipate that some at least of my conclusions will here- after require modification. I regret very much the incompleteness of this report, occasioned in large part by my inability to devote myself longer than a little over five months to the work. My results are derived chiefly from the study of the locust,224 to which I have added a limited number of observations on Anabrus purpurascens. I have endeavored to increase the value of the article by incorporating a considerable number of bibliographical refer- ences. I hope that with these additions this report will assist other American students in becoming acquainted with the present state of our knowledge of the histology of insects without having to search far and wide for the authorities. In brief, I attempt to give a bibliographical index to the general outline of the subject, and to describe in detail such 523 A preliminary report has been published in the First Annual Report of the Commission, pp. 273- 277. 224 The observations aro mostly made of the Caloptenus fcmur-rubrum, the common red-legged locust, and on CEdipoda sordida. HISTOLOGY OF THE LOCUST AND CRICKET. 185 of my own observations as I believe to be new. I shall give a more complete account of the digestive canal than of any other system. The figures on Plates II-VIII are numbered consecutively from 1 to GO. In order to make the relation of the various organs to one another more evident, and at the same time to explain the classification of the tissues, which has been generally adopted upon embryological grounds, I figure and describe two sections through the abdomen of the grass- hopper, Plate II, Figs. 1 and 2. They are both semi-diagrammatic, being intended to represent rather the general arrangement of the parts than their exact disposition in a particular section. To insure accuracy, however, the outlines of both the drawings were made with the camera lucida from actual sections, and these outlines were then changed only so much as was necessary to remove very slight irregularities. Fig. 1 is a transverse section through the abdomen of a female at the level of the posterior part of the stomach. The outer wall I), art., V, is shaded and represented of nearly uniform thickness, which is not quite exact. Outermost is the cuticula, next the epidermis, or cellular matrix, and innermost the muscles—the three parts that make up the outer wall of the body. The same is true of the section through the male, Fig. 2. This section, however, is taken further back in the abdomen, being- through the colon; compare Fig. 45 col. The walls of the abdomen are divided into a large dorsal arch, D, and a smaller ventral arch, F, the two being united on either side by an articulating membrane, art., which will be described in speaking of the cuticula further on. The dorsal arch is really composed of the tergite and the pleurites fused together into one piece.225 Within the body walls, which form, so to speak, a con- tinuous tube, there runs from mouth to anus a second tube of smaller diameter, the digestive canal, the general course of which is shown very clearly in a longitudinal section through a whole grasshopper, see Fig. 45. Iu a transverse section the digestive tract also appears (Fig. 1, St., stomach, Fig. 2, col., colon), separated by a considerable space from the body walls. In this intervening space there lie various other organs, notably those of reproduction. In the female, Fig. 1, it so happens that at the level of the stomach the sexual organs lie above the intestinal canal, while in the male, at the point represented in Fig. 2, the sexual organs lie partly above, partly below, the colon. In the female we notice first the round tubes of the ovary, Ov; second, the ovarian ducts, ovd., and, third, on each side the large uterus, Tit., or upper end of the oviduct, into which the ovarian ducts open directly. In the male, on the other hand, we see the testes, Te., lying above the intestine, the single tubes round in section, being embedded iuor surrounded by connective tissue (Leydig’s zellig-blasiges Gcicebe), and below the colon, col., lie the spermi- ducts or vasa defer entia, (v. def.) Finally, between the inner and outer tubes lie various muscles, the Malpighian vessels, and the numerous branches of the tracheae. These are all left out in the drawing except a Graber Dio Tympanalen Sinuesapparato (ler Ortlioptcren. Denkuchr. Wien. A bad, lid. 36 (1876), p. 75. 186 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. few of the tracheae, Tr., and in Fig. 2 the muscle r. m.y to which I shall refer later. In brief, the grasshopper is built up, 1, of the outer body wall; 2, of the inner tube, digestive canal; and, 3, of the organs which intervene between the two first. Accordingly, I shall describe, 1st, the outer body wall; 2d, the intervening tissue (mesoderm); 3d, the digestive canal and its appendages.220 Before entering into the special subjects, I would remark that the Orthoptera, and indeed all insects, are, it seems to me, remarkably fa- vorable objects for histological investigations. As regards Caloptenus and (Edipoda, it may be mentioned in general that the cellular elements of their bodies are particularly large, and the nuclei of the cells distin- guished by being, for the most part, strikingly granulated and seldom exhibiting distinct nucleoli. ECTODERM. Gutioula.—It is well known that insects have an external crust or shell, the cuticula, which is supposed to always consist mainly of a pe- culiar substance, chitiue, often mingled with earthy salts, such as car- bonate of lime and magnesia. In both locusts and crickets the abdominal segments present differ- ences in the characteristics of the cuticula of different regions. There are at least three distinct modifications—first, upon the dorsal arch; second, on the spiracular or articular fold, which intervenes between the two main arches; and, third, the main portion of the ventral arch— but in the locusts the dorsal and ventral portions are very similar. The dorsal arch, as seen in transverse sections (Fig. 3 d), is much the larger, covering the back and sides of the body, and the articular membrane, art., is a comparatively narrow band. Upon the living locust, or one recently killed, it is easy to observe that the dorsal and ventral arches are movable upon one another in consequence of the extreme elasticity and flexibility of the articular membrane (Fig. C, art.). Both the dorsal and ventral portions of the cuticula are rigid, and, in the locusts at least, present a faint striation parallel to the circumference of the section. This striation may indicate a fibrillar structure. Tlie inner surface of the cuticula presents certain peculiarities in the distribution of a reddish- brown pigment, probably part of the matrix, but otherwise this surface appears quite smooth, while the external surface is somewhat roughened, and is beautifully sculptured in Anabrus, as I will shortly describe. The thickness of the cuticula is about the same in both arches; it has a yellowish tinge, shading off into brown at the posterior edges of the abdominal segments. The rigid portions of the cuticula are further characterized by the pores (Poren-candlchen) and hairs. The pores are quite large in diameter (see Fig. 4 p), and are widened at each end; 220 For tlie relation of those parts the reader may also consult chapter IX of the First Annual Report of the Commission, pp. 257-272. HISTOLOGY OF THE LOCUST AND CRICKET. 187 they always run nearly perpendicular to the surface to the cuticula. Directly over each pore there sits a.stiff chitinous tapering hair (Fig. 4 h and h1), which is generally slightly curved. This relation of the hairs and pores has also been described by Leydig,227 and is well known to naturalists. The hairs are all small, though very unequal in size, the difference in the extremes being much greater than between h and Id in Fig. 4. The hairs do not stand upright, but are so inclined as to point towards the posterior end of the body. Each hair is constricted around its base (Fig. 63 h), forming a narrow neck, below which it expands again, spreading out to make the circular covering membrane of the hair pore. This membrane is very thin, but has a thickened rim. In consequence of this constriction these hairs are commonly said to be articulated. They are not homogeneous, but have a distinct medulla (Fig. 63 h), which is probably a prolonga- tion of the cell which forms the hair. These cells have been described by Graber.228 They were formerly called uIIautdrusenv by Leydig and others. They are, as it were, suspended from the inner side of the large pores as the hairs are from the outer. They are somewhat pear-shaped, and four or five times the diameter of the ordinary epidermal cells, and have correspondingly large round nuclei; their contents are very gran- ular. There are usually two or three, rarely but one nucleus in each hair-cell. Graber suggests the name of trichogens for these cells. They are probably strictly homogeneous with the scale-cells of the Lepidop- tera; the cells differ in the two orders of insects in that they bear a round hair in one case, a flattened hair in the other. The plausibility of this suggestion must, I think, strike every one who is acquainted with the account of the structure and development of the scales in but- terflies given by Semper.229 If the homology is correct, these hair or scale cells must be regarded as specially characteristic of insects, or, possibly, of arthropods generally. The articular membrane, though a part of the cuticula, has either no, or at most very few, hairs. In the locusts the cuticula at the joint is much thicker and paler in color than elsewhere (Fig. 5, art.), being not only thrown up into folds, but also covered with numerous minute pyramidal spines. In the locust the first abdominal segment lacks an independent articular membrane, its own entering into the formation of the sterno- coxal membrane, or articular capsule of the third or metathoracic limb. On the sides of the segment a kidney-shaped piece of the cuticula un- dergoes peculiar modifications to enter into the formation of the tym- panal apparatus. In Anabrus the cuticula presents the following characteristics, besides those which have been mentioned as found in both it and the locusts: First, there are projecting conical nodules scattered irregularly over it, as can be seen in a surface view. (Fig. 59, b b.) These cones are less 227 Ley dig: Lehrbuch tier Histologic, 1857, p. Ill, Fig. 56. Graber: Denk. Wien. Akad., xxxvi, p. 35 (1876). 229 Semper: Zeit. fur wiss. Zool. J3<1. viii, p. 328. 188 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. numerous, much thicker, and shorter than the cutieular hairs. They have rounded apices, and are inclined backward. They do not seem to correspond in an}* way to the hairs, for they do not rest over pores, nor have I seen any specially modified cells underlying them. As far as I have observed, they are mere local irregularities, each nodule being apparently supported by some four or six unmodified epidermal cells.230 The cones in those specimens I have examined are entirely want- ing in the ventral arch, in the upper portion of the dorsal arch, but on the sides of the dorsal arches they are of considerably greater dimensions than upon the spiracular membrane, and finally they are larger and more numerous on the anterior than on the posterior abdominal segments. I have not, however, attempted to follow out the distribution of these structures in greater detail. Second, the whole of the cuticula except the cones just described and the hairs, is divided into numerous minute fields (Figs. 63 and 65), each of which corresponds to a single cell of the underlying epidermis. Each field is bounded by a distinct polygonal outline, and its surface is either covered by a large number of extremely minute projecting points (Fig. 65), as on the dorsal arch, or is smooth as upon the articular membrane and ventral arch. Upon the sides of the dorsal arch and upon the spirac- ular membrane each field has a projecting spine or sometimes two or even three. Fig. 65 represents a surface view of part of the side of one of the dorsal arches. Upon the articular cuticula each spine springs from a short basal collar. Fig. 63 represents a surface view of the upper and anterior part of the dorsal arch. The fine sculpture is drawn only on a few of the fields, none of which have spines. The figure is intended to show that from the smooth circular area around the base of the hairs, h, the fine points of the sculpturing appear to radiate, while elsewhere they are only irregularly distributed. I have been unable to determine how this radiating appearance is caused. The ventral arch has a quite smooth surface and but few hairs. The articular membrane has few hairs, a number of broad cones, and sculp- tured fields, bearing spines, which have a thick collar around their bases. The dorsal arch resembles this membrane generally, but differs from it by the simpler character of its spines, by their absence from its upper portions, and by its brownish tinge. The cuticula between the segments-resembles the spiracular membrane. The cuticula forms also the stigmata or openings of the tracheal sys- tem. Immediately around each opening the cuticula is perfectly smooth, while to form the stigmata it undergoes various modifications, which I have not studied. The cuticula of the thorax, head, and limbs I have not examined. Epidermis.—The cuticula is secreted by an underlying layer of cells, the epidermis proper, often called the matrix or hypodermis, but inas- 21,01 think it possible that the examination of sections, which the imperfect preservation of the parts provente. Zool. Inst. Wien. (1878). 290 A. Gruber: Tiber zwei Siisswasser Calaniden, Leipzig, 1878. Beitrage zur Kenntniss der Genera- tionsorgane der freilebenden Copepoden. Z. Z., xxxii (1879), p. 407. 208 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. in some sections that I could see cilia, but this point I could not settle to my satisfaction. There is a thin, but distinct, layer of connective tissue around the epithelium. The character of the epithelium is not the same throughout this upper division. In the lower part, when seen from the inner surface, the epithelium presents the appearance repre- sented in Fig. 32, the nuclei being oval, of nearly uniform size, and quite closely crowded together. Higher up the nuclei are further apart and vary considerably in their dimensions 5 the outlines of the cells also ap- pear more clearly as pentagonal. Kear the rounded tip the distance apart of the nuclei is still greater, and they are more irregular in size. In some of the specimens I have examined the whole upper division of the tube was crowded with bundles of spermatozoa. In one tube I counted over 200 bundles. The lower end of the upper division tapers off, the nuclei becoming smaller and even more crowded than in Fig. 32. The muscular coat ap- pears thin at first, but, increasing, soon acquires its full thickness, the caliber of the tube diminishing at the same time. A transverse section of this lower part of the vesicula (Fig. 34) shows that the epithelial cells are very much smaller than in the upper portion (compare Fig. 34 with Fig 31, both being equally magnified the walls, however, rendered very much thicker by the enormous muscular coat, Fig 34 Mucr the fibres of which appear to be exclusively circular. I have also made a complete series of sections through the posterior end of the abdomen of the male, some of which display very beautifully the relations of the parts, but these structures are so complicated that an elaborate investigation is necessary to secure a satisfactory interpre- tation of the sections. Therefore I must reserve the subject for another occasion. DIGESTIVE CANAL. Of the digestive canal I shall give a more complete histological description than I have of the other systems. Of the cavity of the mouth and of the oesophagus I shall say but little. The salivary glands I have not studied at all, for want of proper material. Those in the cockroach have been described by von Basch,291 and also in the more recent superb monograph of Kupffer.292 Leydig293 has made some valua- ble observations. The glands have likewise been studied in other insects by various authors, to whom I need not refer here. In order to render my description easier to follow, I will preface my account by a brief review of the divisions of the digestive canal in locusts; my own investigations having shown that the divisions adopted by the older authors,4 and since generally introduced in all text-books,. 291S. Basch: Untemichungen ueber das Chylopoetische und TJropoetische System der Blatta orien- talis. Sitzber. Wien. Akad., xxxiii (1858), pp. 234. Speicheldriisen, p. 235, Taf. v, Fig. 11. 292 Kupffer: Die Speicheldriisen Ton Periplaneta orientalis und ihr Nervenapparat. Beitrage Anat. Phys., C. Ludwig gewidmet, p. 64, Taf. ix. 293 Muller’s Arch., 1859, pp. 59-70. STRUCTURE OF THE DIGESTIVE CANAL. 209 are not quite sufficient. Tlie descriptions, both general and histological, refer to the locusts unless expressly stated to refer to the cricket. The best method with which I am acquainted for readily obtaining a general view of the course and divisions of the digestive tract is the following: Place a female (a male will do, but is not quite so good) in alcohol of about 50 to 60 per cent, for from 12 to 24 hours; then put it in strong alcohol (96 per cent.) for a day or longer; then, with a sharp razor, cut it carefully into halves along the median line, so as to have the right and left sides separately. Lay the pieces under alcohol, and carefully remove the contents of the digestive canal, which will then appear very plainly, its course being as represented in Fig. 45. The cavity of the mouth, M, ascends obliquely forward, and is generally found filled with a black mass, the coagulated u molasses n which grass- hoppers pour out when caught or irritated. The oesophagus, oe., is nar- rower, of uniform diameter, it curves upwards and backwards, terminat- ing very nearly in the center of the head, where it opens into the very large crop, Or. The crop extends through the posterior half of the head and the whole of the thorax; it attains its greatest diameter in the prothorax, behind which it descends, tapering off slightly, and end- ing in the proventiculus, P. The crop itself is divisible into two dis- tinct portions : 1, the anterior (Or.1) lies in the head and prothorax, and is characterized by the somewhat irregular transverse ridges on its inner surface; in Galoptenus spretus, the Eocky Mountain locust, these ridges are somewhat less numerous and powerful than in 0. femur- rubrum; 2, the posterior (Or.2), in which the ridges are longitudinal and much smaller and closer together than in the front segment; the shape of the posterior division is that of a truncated cone. The proventriculus (Kaumagen) P, is so much reduced in the grasshopper that it appears as hardly more than the terminal portion of the crop, instead of being a large and distinct segment of the digestive canal as in other Or- thoptera. The Kaumagen opens into the large u chylific stomach ” or ventricle, ven., which extends along the ventral surface about half the length of the abdomen. At its anterior end it gives off' the six blind pouches, so long known and so frequently described; in a longitudinal section only one of these can be seen (Div.) extending forwards under? neath the crop. The first part of the intestine I propose to call the Ileum, II. It appears at first sight as the direct continuation, or rather as the posterior division, of the stomach, from which, however, it is in reality perfectly distinct, both by its structure and by its separation through a peculiar valve, which I shall describe later. The Malpighian vessels open just underneath and in front of this valve. The second division of the intestine I call the colon, col., a name sometimes applied by older authors to the rectum. The colon is smaller in diameter than any other part of the digestive tube; it ascends and opens into the rectum, B. The rectum extends horizontally directly underneath the dorsum ; its diameter is about two-thirds that of the stomach; its inner 210 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. surface is thrown up iuto six longitudinal folds, the rectal glands, three of which are found in each half-section. The rectum opens into the short anal tube, An., which opens externally on the back just in front of the upper clasper. Crop.—Both divisions have their walls composed of the same layers: 1, an internal chitinous cuticula, which forms the hard covering of the ridges; 2, the underlying epithelium, the matrix of the cuticula, which seems to be pigmented, but unfortunately is not very distinct in my preparations; 3, an inner layer of longitudinal muscles; and 4, an exter- nal layer of circular muscular fibres. The muscular fibres of the crop are all striated. There is a layer of connective tissue between the muscles and the epithelium (Wilde), making five layers in all. As it is not distinct in my preparations I do not enumerate it with those I have myself made out. In the front division the ridges are transverse, somewhat irreg- ular, but each one continuous and not formed of single teeth; they are much more numerous and closely crowded in femur-rubrum than in spretus. The inner covering of the ridges is the thick cuticula. Upon the posterior edge of each ridge there is a row of sharp chitinous spines which point inwards and backwards. The ridges are not all parallel, as is shown in Fig. 45. Those next the oesophagus are broader than the rest and are armed with several rows of spines. The posterior ridges become first slightly irregular, then zigzag, and so gradually change their direction until they become longitudinal and very regularly paral- lel. The area where the ridges are zigzag marks the limit between the two divisions of the crop. The two muscular layers are well developed iu the front division, the longitudinal, which are of course transverse to the ridges, being particularly powerful. The posterior segment of the crop, Fig. 45, Cr.2, has longitudinal ridges. In a transverse section, Fig. 35, it is seen that the ridges are small, rid., rounded on top, with small projecting cuticular spines of yellowish color, s, s. In each ridge the pigmented epithelium appears as a dark layer underneath the cuticula. The inner muscular coat, L, of longitudinal fibres is but little developed in comparison with the enormous coat of circular fibers, nine. G. Thus we see that, in both parts of the crop, that muscu- lar coat obtains predominance whose fibres run transversely to the direc- tion of the ridges. An examination of the inner surface of the hind part of the crop reveals the fact that the ridges are not continuous, but composed of rows of imperfectly individualized oblong teeth, each of which is armed with a few small spines. It will be seen that the general character of the crop is the same as in the cockroach, according to the descriptions of Basch,294 who adds that the epithelium corresponds to Bamdohr’s uflockige-Lage,v and is the same as the membrana propria of Straus-Durckheim and Burmeister. Finally, I must call particular attention to the recent capital memoir295 of 884 S. Baseh. Sitzher. 'Wien. Akad. (1858), xxxiii, p. 242. 285K. F. Wilde? Untersuchungen iiber den Kaumagen der Orthopteren. Arch. f. Jfaturgescli. Jalirg. sliv, 1. Bd., p. 135 (1877). STRUCTURE OF THE CROP. 211 Dr. Wilde, of Leipzig, in wliicli, p. 139, he gives the most accurate account of the crop and provcntriculus of the Acridians and other Orthoptera which has yet been published. The crop of Anabrus is not divided into two parts, and its cuticula forms no ridges, but is divided up into distinct fields (Fig. GO), each of which corresponds to a single epithelial cell, for in preparations colored with logwood, and examined from the surface, a sharply defined, round nucleus appears in the middle of each field. Each field has a spine, which rises from its posterior part and points backward. These spines are more developed than their fellows on the cuticula of the epidermis. The close resemblance of the two cuticulse serves to corroborate the view that the crop of insects arises in the embryo, as a secondary invagination of the ectoderm. Proventriculus.—Dr. Wilde, in the article just mentioned, speaks of the uKaumagenw as the terminal portion of the crop, but I see no ob- jection to considering it entirely distinct and fully equivalent to the pro- ventriculus of other insects with which it is homologous, as Wilde has already pointed out. Wilde appears to have overlooked the fact that it is sharply limited both in front and behind, and in his figure (1. c., Plate IX, Eig. 2) the front limit is not marked. An examination of the proventriculus opened, and spread out so as to expose the inner surface, shows that there are six large teeth, which present a triangular outline, the base facing frontwards, the apex point- ing backwards. The ridges of the crop become zigzag just in front of the bases of these teeth close to which they terminate. Between the single teeth of the proventriculus there are a few parallel ridges, which are not continuous with those of the crop, and which terminate abruptly with rounded ends, at the level of the apices of the large teeth, that is to say at the entrance to the stomach. In the apical portions of the large teeth there is more or less pigment, while in the basal portions there is almost none. The base of the large teeth is notched; the apex rounded off; and their surface covered with a multitude of minute con- ical spines, which project up from the cuticula. In Anabrus the proventriculus is fully developed, and resembles that of other crickets.290' It consists, as in Gryllus domesticus, of two parts: one, anterior, serves as the communication between the crop and the proventriculus proper. This anterior part has no definite limit either in front or behind. Both parts are traversed by six rows of teeth, but, though the rows are continuous, the form of the teeth differs in the two parts. If a single row be examined it will be seen that the change from one form of tooth to the other is gradual, not abrupt. A transverse section through the posterior part of the proventriculus shows the dis- position of the parts to be as drawn in Fig. 58. Externally is the muscu- lar coat, consisting mainly of circular fibres, intermingled with tracheae. I have not succeeded in detecting any longitudinal fibres in transverse 1. c. Arch. f.,Naturgesch., 1877, 1. Bd.,pp. 159-165. 212 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. sections, though in surface views they appear very plainly; inside the coat of circular muscles all the fibres are transversely striated. The teeth form six distinct arches, and are united with the muscular coat only at their sides. The attachments of the adjacent teeth to the mus- cularis are separated by a longitudinal ridge, a, which runs unbroken through the length of the crop, separating the neighboring rows of teeth (compare a surface view Fig. 54 a). Each tooth is tripartite, having a central pointed division, d', and two lateral protuberances, d", which Wilde terms “molar” (mahlzahnartig). The shape of these is best ex- plained by the figure. The whole proventriculus is lined by a contin- uous resistent cuticula, which rests upon a cylinder-epithelium, that varies greatly in height in different regions of the teeth, as is plainly shown in Fig. 58, ep. The epithelium rests on a layer of connective tissue conn., beneath which is the space left by the dental arch; this space, 0, corresponds to a large canal which runs under each row of teeth. Ex- amined from the surface, Fig. 54, the same disposition of the parts can be seen, though less plainly. The central process of each tooth is pointed and inclined backwards, so as to slightly overlap the next following tooth. Certain of the anterior “ molar” protuberances are distinguished from the posterior, by having three dark colored projections of their cu- ticula. The cuticula is armed with spines upon the central dental divis- ion, and with numerous bristles upon the “molar” protuberances and interdental ridge. A side view, Fig. 55, is also given in order to make the relation of the teeth to one another as plain as possible. In the anterior part of the proventriculus the teeth are simpler in form, and the longitudinal ridge and “ molarv protuberances are want- ing. The cuticula gives off a dense coat of long hairs. The edge of each tooth is deeply serrated on both sides of its point, instead of being merely somewhat roughened as in the posterior part. Finally these an- terior teeth are convex on their front, concave on their hinder sides. They become smaller as we go forward, the rows spreading apart as they widen out to form the crop. Posteriorly the rows of teeth stop quite suddenly. The interdental ridge runs somewhat further on, and is rounded off at its termination. On the last five or six teeth the middle process gradually loses its prom- inence, and on the last two the “ molar ” processes are also very much re- duced. The total number of teeth in each row is twenty three or four, of which eight or nine belong to the anterior and fifteen to the posterior division. In Grijllus campestris and domesticus the crop, likewise, forms two divis- ions, in the posterior of which there are fifteen teeth in each row. It is to the posterior division alone that Wilde (1. c.) restricts the name pro- ventriculus, but I cannot see what grounds he has for so doing, for the two parts have essentially the same characteristics. Stomach.—This name I apply to the ventriculus of authors, the Chy- lusmagen of the Germans, Fig. 45, ven. Of no part of the digestive STRUCTURE OF THE STOMACH. 213 canal is our present knowledge so unsatisfactory as of this. The few observations that have been made are eminently incomplete. It is known that there is no thick cuticula; that the muscular layers are less powerful than in other parts, and certain other details, which a brief ex- amination suffices to clear up. Frey and Leuckart297 pointed out that the walls of the stomach were not folded, but that the secretory surface was increased in some cases (in many Coleoptera, for instance) by the epithe- lium and connective tissue forming villi, a fact already noticed by H. Meckel.298 Sirodot299 subsequently showed that there are also gastric glands in many insects, and describes particularly (1. c., pi. 13, Fig. 3) how in the field cricket the gastric follicles occupy the interspaces of a network formed by the sinuous fibers of the connective tissue, “ tunica propria ” auct. I have found essentially the same structure to exist in grasshoppers (Galoptenus and Oedipoda). The description of the minute anatomy of the veutriculus which Leydig gives300 is very meager and insufficient, while that given of the epithelium and glands in the stomach of the cockroach by von Basch301 will probably require some modification. The walls of the stomach are composed of an internal epithelium, a layer of connective tissue, an inner layer of unstriated circular muscu- lar fibres, and an external layer of longitudinal fibres of striated muscle. In studying these layers I have found it best to begin by viewing them from the inner surface. If the walls of the stomach be spread out and stained and then mounted in glycerine or Canada balsam, it will be seen that the nuclei of the epithelium are not uniformly distributed, but there are little clusters, each of which corresponds to a small gland or follicle; it can be further seen that each gland has a cavity or duct; each follicle lies in a cup of connective tissue, which separates it from its neighbors. If a piece of the wall spread out on a glass slide in a drop or two of water, is gently brushed with a fine camel’s hair pencil, the epithelium can be removed, and if the specimen be then stained and mounted the structure of the remaining layers will be displayed as shown in Fig. 39. The connective tissue, tunica propria, forms a somewhat irregular net- work,302 the meshes of which vary in size only between certain limits. In the figure the network is drawn somewhat darker than it appears in reality, in order to make it stand out more plainly. The spaces of the network are the cups before mentioned in which the gastric fol- licles lie. The tissue has a fibrous character and also forms the bottoms of the cups, as is shown by sections. Underneath the connective tissue follows the internal muscular coat, In. m., composed of a great number 297 Frey und Leuckart: Anat. Physiol. Ubersicht.- Thierreichs, 1855, p. 114. ms2Ieckel. Mikrographie einiger Driisenapparate niederer Seethiere. Muller’s Arch., 1846. Die Ein- theilung des Darmcanals bei den Insekten. Par. 4, p. 23. 209 Sirodot Eecherches sur les secretions chez les Insectes. Ann. Sci. Nat. Zool. Ser. 4. Tome X, p. 183 (1858). 300 Ley dig. Lehrbuch der Histologic, 1858, p. 337. 301 Basch, 1. c., Wien. Akad. Sitzber., xxxiii, 248,ff 302 Compare Sirodot, 1. c., PI. 13, Fig. 3. 214 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. of pale fibres, running singly, and parallel to one another around the stomach. Between this layer and the tunica propria there are some in- distinct longitudinal fibres that may be muscular; these fibres also ap- pear in transverse sections. If my supposition as to their nature is correct, then there are two layers of unstriated muscles, the longitudi- nal layer being innermost, just as wre found with the striated muscles of the oesophagus. Most externally are the longitudinal striped muscles, which are distributed in single bundles (L, L,) and do not form a con- tinuous layer. Each bundle is composed of a number of fibres and pur- sues its own course; the bundles are not parallel, as will be evident upon glancing at the Fig. 39; sometimes two bundles unite, or one bundle connects two others; in spite of these irregularities, however, the trend of the muscles is lengthwise of the stomach. Finally, it must be men- tioned that numerous tracheal branches penetrate the muscular layers and ramify both through them and also through the connective tissue. A transverse section (Fig. 3G) through the walls of the stomach exhib- its further structural features. The epithelium is composed of cylindri- cal cells, with large, finely granular nuclei, in some of which a nucle- olus can be distinguished; the limits of the single cells are not well defined. The follicles are formed by simple involutions of the epithe- lium, there being no apparent change in the general character of the cells except in their shape, wThich is not plain enough in sections for me to describe it with real accuracy. They are, however, certainly not spherical, as affirmed by Sirodot. The epithelium is covered by a cuti- cula, cu., which also descends into the follicles, and is traversed by nu- merous pore-canals. I cannot make out any basement membrane, but apparently the epithelium rests immediately upon the connective tissue, conn. The manner in which this layer extends up between the follicles is seen very plainly in transverse section; it is comparatively thin, as is also the circular coat, muc., of unstriated muscles. In the part figured it so happens that there are no longitudinal bundles of striated muscle, but the tracheae, TV., appear very distinctly. The ventricle of Anabrus differs from that of the locusts, as far as I have observed, only in unimportant details. The diameter of the glands is somewhat greater, as shown by the size of the u cups ” of connect- ive tissue (Cf. Figs. GG and 39) in which they rest. The longitudinal muscles form more regular bundles than in the locusts, and fibres cross less frequently from one bundle to another. Diverticula.—I employ this name for the six caecal pouches, frequently called the appendices ventriculares. It has been commonly stated that these caeca do not differ in structure from the stomach, a statement which, though quite incorrect, is repeated even by so exact an author as Milne- Edwards, in his magnificient compilation of Anatomy and Physiology.303 Yet, that there is a great difference, had been noted in 1846 by H. Meckel,304 303 Milne-Edwards: Lemons sur la Physiologie. Tome v., p. 608-609. 804Meckel: Hiiller’s Arch., 1846, p. 38 ff. STRUCTURE OF THE GASTRIC CCECA. 215 whose observations are also cited by Ley dig on p. 337 of his “ Hand- buck” Sirodot305 repeats the old and incorrect statement, while Graber306 expressly states that their structure is not the same as that of the stom- ach, and that they are not u einfache Aussackungen des Cliylusmagens.” More recently M. F. Plateau30" has again called attention to the incorrect- ness of the old view. In fact, a single transverse section of one of the diverticula (Fig. 37) demonstrates at once that its structure is entirely different from that of the stomach. Its inner surface is thrown up into longitudinal folds, generally twelve in number. These folds shine through the outer walls, and are, accordingly, indicated in the drawings of Dufour, Graber, and others. The whole diverticulum has an external muscular envelope, out- side of which are a few isolated longitudinal muscular bands. The folds within are formed mainly by the high cylindrical epithelium, which lines the whole interior of the cavity. The shape of the folds will be more comprehensible from the Fig. 37 than from any description I can give. They are not all of the same height, but they form two op- posite groups, the folds in the center of each group being the highest. On either side and between the two groups there are smaller folds. Whatever the height of the folds, however, they all have the same gen- eral histological character, which is indicated by Fig. 38. The cells are large and cylindrical, slightly granular, those near the top of each fold being slightly pigmented with brownish matter that obscures their definition. The nuclei are large, oval, coarsely granular, and lie in the middle or lower parts of the cells. The cells are protected by a delicate but very distinct cuticula, in which I can detect no pore-canals, though it otherwise resembles the cuticula in the ventriculus. In the center of each fold there runs up a thin partition of fibrous tissue (Fig. 38, conn), which separates the epithelium of the two sides, and is itself an off- shoot of the connective tissue, tunica propria, that intervenes between the muscles, muc., and the epithelial layer. The tracheae ramify through- out all the layers outside the epithelium; one of the main trunks run- ning to the wall is shown at Tr. (Fig. 37). It sometimes looked as if there were glandular follicles in the bottom of the spaces between the folds, but of this I could not make sure. Towards the tips of the diverticula the folds decrease in height as the diameter of sacks diminishes, until finally they disappear almost com- pletely. Gastro-ileal folds.—I have now to speak of some very curious and striking.formations which seem to have escaped notice until now, for I find no description of them in any of the works on insect anatomy which 305 Jj. e.y p. 157. 306 y. Graber: Zur niiberen Kenntniss des Proventriculus und der Appendices ventriculares bei den Grillen nnd Laubheuschrecken. Sitzber. Wien. Akad. (1869), lix, p. 33. 307F. Plateau: Recherches sur les Phenomfenes de la Digestion cbez les Insectes. M6moires Acad. Eoy. Belg. (1875), tome xli, p. 75. 216 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. I have been able to consult. It is impossible to follow Dufour’s account308 of the termination of the stomach and the origin of the intestine, for it seems to me not only incomplete but also inaccurate. I have already referred to these folds, p 209, as the valve which marks the termination of the stomach. They are indicated in Fig. 45 as six dark spots, round in front, and lying at the anterior end of the ileum, II., so as to form a ring around the interior of the intestine. If this part of the digestive tract be opened, spread out, colored, and mounted, it will appear as represented in Fig. 46. In front lies the stomach, vcn., from which the epithelial lining has been removed, and which can therefore be readily recognized by the network of connective tissue before de- scribed and the isolated, longitudinal, muscular bundles. Behind the protuberances comes the ileum, 17., which is traversed by six broad and low longitudinal folds, three of which appear in the figure. On the line between the ileum and the ventricle lie the strongly pigmented gastro- ileal folds. They are twelve in number, and all alike. Their shape is best indicated by the figure. They are rounded off in front, where they are broadest and stand up highest; they narrow down backwards; the pigment disappears, and they gradually fade out into the ileal folds; directly underneath them, and just at the posterior termination of the ventricle, there is a strong band oif circular striated muscular fibers 0.14 mm wide. These folds are found in G. femur-rubrum, C. spretus, and (Edipoda sordida, and probably in all grasshoppers. I have made sections of them from Edipoda, Figs. 49, 43, and 44. Fig. 49 shows the general arrangement of the folds ; there are twelve of them, all pedunculated with broad tops and thick stems. They are covered with an epithelium, the cells of which are smaller and for the most part not pigmented be- tween the folds, and larger with a great deal of pigment on the folds, as also appears in Fig. 45. The muscular coat, muc., is very powerful, and of even thickness throughout. Between it and the epithelium there is a well-developed tunic of connective tissue. Examined with a higher power it is seen, Fig. 44, that the epithelial cells are large, with an oval nucleus in the lower half of each cell. The cells in the valleys are not so high as on the folds, though the nuclei are not any smaller. The epi- thelium is covered by a thin cuticula, which is armed on the surface of the folds with minute conical spines, Fig. 44, cu., which are generally, but not always, wanting between the folds ; the spines are sharp-pointed and inclined backwards. The connective tissue is fibrous, and contains a good many small, granular, oval nuclei. The layer of circular muscles is composed of three or four parallel layers of bundles. I think there are some few longitudinal fibres between the muscular coat and con- nective tunic. Beturning now to the epithelium, we find cells in all stages of pig- mentation. The pigment is in fine granules of various sizes; they first 308Dufour, Surles Orthopt6res, 1. c., p. 314. STRUCTURE OF THE INTESTINE. 217 collect around tlie nucleus, Fig. 43, and as they accumulate they extend through all the rest of the cell, except the upper part underneath the cuticula, which portion always remains clear, as is seen in Fig. 44. Viewed from above the epithelial cells appear as polygonal pigmented fields, each separated from its neighbors by a clear line. Posteriorly the cells become less and less pigmented, and pass by gradual changes into the epithelium of the ileum. Ileum.—The ileum is traversed by six longitudinal folds, with inter- vening furrows. Outside each furrow is a longitudinal muscular band. Viewed from the inner surface, the epithelium is seen to have an unusual character. The cells in the middle of each of the flat folds are quite large {Fig. 50 A), polygonal in outline, with large, round, granular nuclei, which stain very darkly with hsematoxiline. Toward the furrows the cells be- come very much smaller, those at the edge of the furrow being not more than one-sixth the size of those in the middle (Fig. 50 B). Underneath the furrow, the longitudinal muscles (Fig. 50 L) are seen shining through. A transverse section (Fig. 51) shows that the walls are double; the inner leaf is composed of epithelium, Ep., and connective tissue, the outer leaf, of the circular muscles, muc. C. The furrows are indicated by the six bands of longitudinal muscles, L L. It is only opposite these bands that the two leaves are united, as is shown more plainly in Fig. 52. The epithelium, Up., rests directly upon and is intimately united with the connective tissue, so forming a single leaf, which then bends down, mak- ing a furrow, U, opposite the longitudinal muscle, L L, where it is united with the circular muscular layer, muc C. The consequence of this ar- rangement is that underneath each fold there is a very large longitudi- nal cavity between the 'propria and the muscularis. The cuticula (Fig. 52), cu., is thin, but probably chitinous; it resembles that on the gastro-ileal folds, except that there are no spines, but it is not in the least like the ventricular cuticula. It extends equally over the folds and the furrows. The epithelium has round nuclei; the size both of the cells and of the nuclei diminishes rapidly towards the bottom of the furrows (Fig. 52), F. The bases of the cells are somewhat dome-shaped. The nuclei are sur- charged with granules, and have a less distinct outline than the nuclei from other parts of the body. The circular muscles are moderately developed. Each longitudinal muscular band consists of 10 to 15 single bundles. The fibres are striped. Colon.—In the colon the six longitudinal folds of the ileum are con- tinued, but their surface, instead of being smooth as in the ileum, is thrown up in numerous irregular curved and zigzag secondary folds, as is imperfectly indicated in Fig. 2, col. The cells of the epithelium are of uniform size, and contain, especially at the summits of the secondary folds, pigment granules like those in the cells of the gastro-ileal valve. The epithelium is covered by a highly refringent cuticula without spines, 218 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. and, like that on the ileum, it rests upon a layer of connective tissue, beyond which follows (1) an internal coat of longitudinal, and (2) an ex- ternal coat of circular muscular fibres, which are striated. Rectum.—The rectum of insects is remarkable for containing certain curious structures now generally known as rectal glands. They are in- cidentally mentioned by older authors, but Frey and Leuckart 309 were, as far as I am aware, the first to recognize their general distribution and importance. Leydig310 was the first to give an accurate account of their histological structure. Since then they have received but little atten- tion until 1876, when Dr. Chun published his investigations,311 which were made under the guidance of Professor Leuckart. Chun extended his researches over a variety of insects, but gives no account of the glands as found in the grasshoppers, though he studied the closely allied Katy- did (Locusta viridissima, 1. c., p. 32). He describes the glands as six flat folds, formed by a high epithelium and well-defined cuticula; the con- nective tissue (tunica propria) is largely predominant; there is a coat of circular muscular fibers, and six external longitudinal muscular bands, corresponding to the furrows between the glands. This description is applicable also to the grasshoppers I have investigated, the only differ- ences being in the structural details of the single layers. Seen from the inner surface the epithelium presents a most curious and puzzling aspect, Fig. 53, because there are two kinds of nuclei at different levels; small, spherical nuclei nearest the surface, and larger nuclei of oval form deeper down. The small nuclei are less numerous than the large; in the portion represented in Fig. 48 there are 21 small aud 49 large nuclei, or, in other words, less than half as many of the superficial as of the deep nuclei. As the two sets are at different levels they cannot both be in focus at once, hence in drawing Fig. 53 with the camera-lucida, the large nuclei were first focused and drawn, and then the smaller nuclei were drawn in the same way over the first. When we focus upon the large nuclei, the polygonal outlines of the cells can be seen in successful preparations as repre- sented in the figure; as there are no spaces between the cells with the large nuclei, the cells belonging to the small nuclei do not extend so far down, though the cells of the large nuclei do reach up among the small nuclei, as can be seen in sections. The outlines of the cells to which the small nuclei belong, I have not been able to distinguish. The small nuclei are spherical, very refringent, and have a sharp out- line. The large nuclei are oval, their long axes lying generally length- wise rather than transversely on the folds of the rectum. An epithelium presenting a somewhat analogous peculiarity has been described from the epididymis of mammals by Klein.312 He figures small darkly stained 309 Frey and Leuckart: TJebersicht des Thierreichs, 1855, p. 116. 310 Ley dig: Lelirbuch der Histologie, p. 337. 3110. Chun: Ueber den Bau, die Entwiekelung unci pliysiologische Bedeutung der Kectaldriisen bei den Insecten. Ahh.: Senckb. Xatforscli. G-es. (Frankfort) Bd. x, p. 27, mit drei Tafeln. 312 Klein: Observations on the structure of cells and nuclei. Quart. Journ. Micros. Sci., XIX, (1879), p. 138, pi. VII, fig. 9. THE DIGESTIVE CANAL AS A WHOLE. 219 cells lying at the bases of the high columnar ciliated epithelium. It is, however, uncertain whether these small cells lie between the others, or form a sub epithelial endothelium, similar to that described by Debove.313 Underneath the epithelium appear the round nuclei of the tunica propria, and the very much elongated nuclei of the tracheal ramifica- tions. In a transverse section, Fig. 42, it is seen that each gland is a low flat fold of the epithelium; each fold is separated from its neighbor on either side by a deep but narrow furrow, F, F', and is covered internally by a cuticula, which is quite resistent, highly refringent, and very slightly tinged with yellow. The epithelium, Fig. 41, is, as was to be expected from the presence of the two sets of nuclei, composed of two kinds of cells; 1st, cylindrical cells corresponding to the oval nuclei; in sections these nuclei appear round and are seen to lie in the basal por- tion of the cells; 2d, cells corresponding to the superficial nuclei; each of these nuclei is surrounded by a clear space, as indicated in Fig. 41, but this space has not a sharp outline as there represented ; the shape of these cells I have been unable to determine. The epithelium rests upon a layer of connective tissue, in which there are round granular nuclei, as before stated. Outside of the connective tissue there is a thin layer of circular muscular fibres, Fig. 42, muc. The tracheae, with their distinctive nuclei, ramify throughout all parts of these two layers. Opposite each furrow there is a longitudinal mus- cular band, Fig. 42, L 77, composed of some twenty or more striated bundles. Attached to the outer walls are found large tracheal trunks, TV., and Malpighian vessels, M. v. At the points where the epithelium of the folds descends to form the intervening furrows, there is a little accumulation of pigment granules. From the above description it will be seen that the rectal folds do not offer the least appearance of glandular structure; neither is any evi- dence deducible from their microscopic anatomy to indicate that their function is that of absorption. Neither does it appear to me that Chun, in his memoir, has elucidated their function in other insects, and the opinions he expresses with apparent confidence I cannot regard as any- thing more than speculative. SUMMARY OF OBSERVATIONS ON THE DIGESTIVE CANAL. If we now glance back at the descriptions above given of the histo- logical peculiarities of the various divisions of the digestive canal, there are certain general features which deserve especial attention. In the first place it will be recognized that the digestive tract is composed of three main divisions: 1, the oesophagus, crop, and proventriculus; 2, the ventricle and diverticula; 3, the ileum, colon, and rectum. In the first division there are two coats of muscles, an internal longi- sl3Debove: Memoire sur la couche endotlieliale sous-Cpitlieliale des membranes muqueuses. Arch, do Physiol., 1874, p. 19. 220 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. tudinal and external circular coat; the fibres are all striped. The lining epithelium is not much developed, but forms a thick, hard, and very re- fringent cuticula that is thrown up into ridges, that may be armed with spines. The chitinous lining, or the cuticula, is undoubtedly always secreted by an epithelium,314 and does not belong in the series of con- nective tissues, as Leydig has maintained.315 It will be seen that these features are common to all the subdivisions of the anterior segment of the digestive canal, the principal variations being in the form and develop- ment of the ridges, and the muscular layers, as I have already described in detail. The thick cuticula of the u Vorderdarm” has been observed in many insects,316' and of all orders. The second division of the alimentary canal is distinguished from the first by the epithelium being composed of very high cylindrical cells, which make up the greater part of the thickness of the walls; by the pres- ence of a very delicate, and but slightly refringent, cuticula, and the ab- sence of ridges; by the unstriated muscular coats, and, finally, by the development of glandular follicles and folds. The ventricle and divert- icula have all these peculiarities in common, while no other part of the digestive canal resembles them in the least. Essentially the same pe- culiarities distinguish the “Mitteldarm” of Phthirius inguinalis, Leach317, except that there are no glandular follicles. Landois318 has wrongly ho- mologized this part with the crop of the Orthoptera. The third division (intestine and rectum) has an epithelium, the cells cf which are intermediate in size between those of the first and second division. The cells are often pigmented; they are covered by a cuticu- la much firmer than that of the ventricle, but not so thick and hard as that of the first division. The very refringent cuticula is not trans- formed into ridges, though in some parts it is covered with delicate conical spines, which are very short. The epithelium and underlying connective tissue (tunica propria) are thrown up into six folds, which run longitudinally, being regular in the ileum and rectum (as the rectal glands), but very irregular in the colon. Outside the depression between each two neighboring folds there is a longitudinal muscular band, thus making six bands. This peculiar disposition of the longitudinal muscles does not occur in any other part of the canal; it is therefore especially characteristic of the third division. From this statement of the charac- teristics of the three divisions, it is evident that the gastroileal valves belong to the third. The curious repetition of the number six may be pointed out here. I cannot but think it will be ultimately found to have some hitherto un- suspected meaning. There are six rows of teeth in the proventriculus, 314Semper: Ueber die Entstehung der Scliuppen bei den Lepidopteren. Zeit. Wias.Zool., VIIL Cf. also, Gegenbaur, Chun, Braun, et al. 3lBLeydig: Vom Bau des Thierschen Kbrpcrs, p. 38, ff. 316 For example: Phthirius inguinalis Leach. Graber. Z. Z. XXII, 141. 31J Oraber: Zeit. Wiss., Zool. XXII, 142-144. -318 Lcmdois: Zeit. Wiss. Zool., XIV, p. 1, and XV, 502. THE DIGESTIVE CANAL AS A WHOLE. 221 six diverticula arising from the stomach, and twelve longitudinal folds in each diverticulum. There are twelve (twice six) gastroileal folds, ar- ranged in twos, each pair appearing as the double anterior termination of one of the six ileal folds, which, changing their character, extend backwards through the colon; finally, in the rectum there are six rectal glands. The three divisions of the digestive canal are perfectly natural; their existence of itself suggests that they represent the three segments which are usually distinguished upon embryological grounds, namely, the fore- gut, midgut, hindgut (Vorderdarm, Mitteldarm, and Hinterdarm). This supposition is strengthened by Bobretzky’s319 observation that in dec- apods the embryological foregut forms the oesophagus and Kaumagen, while the midgut forms the follicular stomach and diverticula (liver). This is a strong confirmation of the conclusion that I have been induced to consider probable upon purely anatomical grounds. It seems to me, moreover, that Hatschek’s320 observations also point to the same conclu- sion, viz, that the ventriculus (Ghylusmagen), together with its append- ages, represents the midgut, all in front being foregut, and all posterior to it arising from the hindgut. The principal respects in which the middle division differs from the other two is by, 1, its glandular character; 2, the presence of a delicate cuticula, probably not chitinous; and, 3, of unstriated muscles. It seems to me now a legitimate problem in insect anatomy to determine whether these characteristics are applicable to the midgut of all insects. In all parts of the digestive tract the succession of the layers is the same: 1st, a cuticula; 2d, an epithelium; 3d, connective tissue; 4th, muscles. Besides which there is stated to be a pavement epithelium (serosa) outside the muscles in some insects. This I have not observed in the grasshoppers, though it may be present. Of the physiological functions of the single parts of the digestive canal little is really known, though some observations have been pub- lished by Sirodot and Plateaux. I should like to interpolate here a comparison, which is curious and odd rather than of scientific value. After Malpighi had shown that the grasshopper had several stomachs, some of the older authors, according to Colin, considered these insects to be ruminants, comparing the vari- ous parts of their digestive canal with the divisions of the stomach in the true ruminants. Of course this idea is now entirely rejected, but it is nevertheless curious to notice that with our present knowledge we can trace an analogy between the crop and the rumen, the ventricle of the grasshopper and the sheep, while the diverticula with their leaf-like folds singularly imitate the structure of the psalter. Those who are not familiar with the anatomy of ruminants, will find a clear and excellent account in Huxley’s Anatomy of Vertebrated Animals. 319 Bobretzky: Zur Embry ologie der Arthropoden (in Russian) as abstracted by Hoyer in HoiFmann und Schwalbe. Jahresbericht der Physiol, u. Anat. fur 1873, p. 314. 330 B. Uatschek: Beitrage zur Entro. Lepidopteren. Jena Zeitschr. Bd. XI. (1877), (p. 17 des Separatab- druckes.) 222 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. MALPIGHIAN VESSELS. The vasa varicosa of Malpighi have long attracted the attention and excited the interest of naturalists. The earliest histological description of .them, however, with which I am acquainted, is comparatively recent— I refer to the article of H. Meckel.321 Since then three general accounts of their structure have been published, one very full by Sirodot,322 and another by Leydig,323 and the third and most important by Schindler,32* and they have been investigated by numerous other anatomists in a great many insects. Their structure is very much the same in the grasshopper as in the cockroach.325 They are covered by a delicate external envelope (tunica propria), Figs. 40, 41, 47, 48, in which there occasionally appear small nuclei. They are lined by flattened epithelial cells with granular con- tents and large oval nuclei, which leave a rouud central cavity, Fig. 40. The canal, as observed in optical section, Fig. 47, is not straight, but somewhat sinuous in its course. Seen in transverse section, the out- lines of the cells, Fig. 40, resemble those of truncated cones. There are generally four rows of cells around the inner canal, as indicated in Fig. 40. Some parts of the vessels are surcharged with reddish-brown pigment granules. The tubes are, as is well known, not of the same diameter throughout their length, but consist of a narrower and a wider portion. The Figs. 40, 42, 47, 48 all represent the narrower part. In the segment with the greater diameter the thickness of the walls remain about the same, so that the “lumen” of the vessel is increased. The nuclei are larger and more nearly round instead of oval. 321 Meckel, 1. c., Muller’s Archiv. 1846, p. 41 ff. 322 S. Sirodot: Reeherclies sur les S6cr6tions cliez les Insects. Ann. Sci. Nat. Zool. S6r. IV. Tome x (1858), p. 251. Histologie, p. 268. 323Ley dig: Lehrbuch der Histologie, p. 464, § 426. 324 E. Schindler: Beitrage zur Kenntniss der malpighischen Gefasse der lnsecten. Zeit. f. wiss. Zool., Bd. xxx. (1878), p. 587. 32SBasch. 1. c. Sitzber. Wien Akad. xxxiii. (1858), p. 254. EXPLAXATIOX OF PLATES II-VIII. All the figures on Plates II-VII, except those specially otherwise designated, are taken from preparations made from Caloptenus femur-rubrum. The figures on Plate VIII, are all from Anabruspurpurascens. All but three or four of the figures were drawn in outline with the camera lucida, and the details added afterward with free hand. The drawings, with the partial exception of Fig. 58, are nowise diagrammatic, but fall short in clearness of the actual preparations. EXPLANATIOX OF THE LETTEPJXG. An., anus. art., articulating mcmbran lid., muscular band. ch., cord of ovarian tube. col., colon. conn., connective tissue. Cr.,1 Or.,* crop, 1st, 2d segment. cm., cuticula. cijs., wall of spermatocyst. I)., dorsal arch of body wall. d.‘, d.", dental processes. Dh\, diverticulum of stomach. 1). It., dorsal nerve roots. lu/., egg. Ej. D., ductus ejaculatorius. Ep., epithelium. furrow between intestinal folds. Gr., granular layer, inside epithelium. G. Z., ganglion-cells. h. h.‘, cuticular hairs. II., ileum. In. m., internal muscular coat. L. longitudinal muscles. M. mouth. mac., muscle/. nine. C., circular muscles. M. v., malpighian vessels. Oe. oesophagus. Or., ovary. Ord., anterior ccecum of oviducts P., proventriculus. ])., pore canals. r. m., musculus respiratorius. rid., cuticular ridges. Te., testes. # Tv., tracheae. Tu., external tunic. Ut., utents. ¥., ventral arch of body wall- Ven., ventriculus. V. R., ventral nerve roots. V. sem., vesicnlse seminales. PLATES II-VI, CALOPTENUS AND OEDIPODA; PLATE VIII, ANABRUS. PLATE II. Fig. 1.—Section through, the abdomen of a female at the level of the posterior part of ventricle. D., Dorsal arch; V., ventral arch; Ov., ovary; Ovd., blind end of oviduct; Ut., uterus; Tr., trachea; art., articulation between dorsal and ventral arches; St., stomach. Fig. 2.—Section through the abdomen of a male at the level of the colon. D., dorsal arch; V., ventral arch; art., articulation between the two arches; Tr., tracheae; Te., testes; col., colon; r. m., respiratory muscle; V. sent., ves- iculae seminales. Fig. 3.—Section of cuticula of abdomen. Letters as before. Fig. 4.—Section of cuticula, p. p., pore canals; li. li.', cuticular hairs. Fig. 5.—Transverse section of wing muscles. Fig. 6.—Part of transverse section of abdomen to show the respiratory muscle r, m. ; D., dorsal arch; ¥., ventral arch; art., articular membrane; Ep., epider- mis; cm., cuticula; li., hairs; conn., connective tissue. Fig. 7.—Fine tracheaB of rectum; n.', triangular nucleus in fork. Fig. 8.—Tracheal branchlet. Fig. 9.—Bundle of striated muscle from the head. Fig. 10.—Spiral trachea of malpighian vessel. Fig. 11.—Diagrammatic section of last ventral ganglion; D. R., dorsal roots; V. R., ventral roots; G. Z., ganglion cells. Fig. 12.—Ramification of tracheae in muscles; s, fine terminations. Fig. 13.—Ramification of tracheae on the ovary. U. S Entomological Commission Vol. 2 Flale II. Fig. i 'ngs Fig 3 fig-6 Fig.7 ng. 2 Fig. 8 r-g9 ng. ft F^.IO rig. II Fig. 13 CS. Minot, del. HISTOLOGY OF THE LOCUST Ik" SincL'i” Sc See liifc. I’Iilu. PLATE III. FlG. 14.—Ramification of tracheae on the oviduct (uterus.) FlG. 16.—Connective tissue cells (fat body ?) from between the seminiferous tubes. Fig. 16.—Section of a ripe ovarian follicle; Eg., egg; Sh., shell (?) secreted by the epithelium, Ep. Fig. 17.—(Edipoda sordida. Connective tissue around the ovary. Fig. 18.—CEdipoda sordida. Epithelium of uterus seen in section. Fig. 19.—Transverse section of a whole, ripe ovarian follicle ; Eg., egg; Ep., epithe- lium. Fig. 20.—Surface view of the follicular epithelium of the ovary. FlG. 21.—(Edipoda sordida. Inner surface of uterus. L S. Entomological Commission. Fi& 16 Vol. 2 Plate III. 14 Fig. 15 F14.I7 fij- 18 Fifr'S F,£.-Zl Fig. 20 (.' S Minof.. del. HISTOLOGY OF THE LOCUST TK« Sinclair * . li;h, Pbfla PLATE IY. Fig. 22.—(Edipoda sordida. Longitudinal section of the uterus; Gr.f granular layer; Ep., epithelium; conn., tunica propria; muc., longitudinal muscular coat. Fig. 23. Edipoda sordida. Surface view of uterine epithelium. Fig. 24. Section through the upper part (first segment) of seminiferous tube; Cys., walls of the spermatocysts; Tu., external tunic. Fig. 25.—Caloptenus spretus. Seminiferous tube, isolated; conn., connective tissue; I, II, III, and IV, the four segments of the tubes. Fig. 26.—Young spermatoblast. Fig. 27.—Spermatoblasts just divided. A, Spermatoblast in process of dividing. Fig. 28.—Older spermatoblasts. Fig. 29.—Transverse section of bundle of young spermatozoa. Fig. 30.—Transverse section of older bundle. Fig. 31.—Section of the upper part of a vesicula seminalis. Fig. 32.—Epithelium of the upper part of a vesicula seminalis. Fig. 33.—Transverse section of the ejaculatory duct, Ej., D; Ep., epithelium; muc., circular muscle; Tr. Tr.', tracheae. Fig. 34.—Transverse section of the muscular portion of a vesicula seminalis. U S Entomological Commission VoL 2 Plate IV. Fi'l 22 Fig. 26 F,g.23 Fig. 24 Fig 2.6 F,|. 27 Fig 28 Fi£27 Fi£ 39 H 3° FitF 32. Fife.3l Fi£. 33 34 < S Mi not. dal. HISTOLOGY OF THE LOCUST. ».? ijanctai t Ssti.lii. OSU Fig. 35.—Transverse section of the hind part of the crop. Sa., spines; rid., ridges; L., longitudinal; muc. C., circular muscles. Fig. 36.—Section of the ventricular wall; d., duct of follicle ; cu., cuticula; Ep., epi- thelium; conn., connective tissue; muc., muscles; Tr., tracheae. Fig. 37.—Transverse section of a diverticulum. Tr., trachea; muc., circular muscular coat. Fig. 38.—Section of a single fold of a diverticulum ; conn., connective tissue or tunica propria. Fig. 39.—Inner surface of ventricle, with the epithelium removed. In. m., circular; L., longitudinal muscles. Fig. 40.—Transverse sections of three Malpighian vessels lying against the muscular walls of the rectum, red. Fig. 41.—Caloptenus sprctua. Section of the epithelium of the rectum. Fig. 42.—Transverse section of rectal folds. F. F.1, furrows between the folds; L. L., longitudinal muscle; M. v., Malpighian vessels. PLATE Y. U. S. Entomological Commission Vol. 2 Plate V. Hg. 35 Fig-37 Fig 36 Fig. 38 Fig. 39 fig- 4C Fii.4Z Fi£.4l OS. Minot del. Tiins Sinclair A Sob . lith, Phila HISTOLOGY OF THE LOCUST. PLATE VI. Fig. 43.—Oedipoda sordida. Epithelial cells of gastro-ileal folds. Fig. 44.—Oedipoda sordida. Part of transverse section of gastroileal folds; cu., cutic- ula; muc., muscle. Fig. 45.—Longitudial median section of Caloptenus femur-nibrum, female, to sliow the digestive canal. M., mouth; Oe., oesophagus; CV.1, anterior; CV.3, posterior division of crop ; p., proventriculus; Div., diverticulum ; Ven., ventricle; II., ileum; col., colon; E., rectum; An., anus. Fig. 4(5.—Surface view of the gastro-ileal folds. Ven., ventricle ; lid., circular muscu- lar hand under the folds ; II., ileum. Fig. 47.—Optical section of Malpighian tube. Fig. 48.—Malpighian vessel. Fig. 49.—Oedipoda sordida; transverse section of gastro-ileal folds; muc., muscular band; Bd., of Fig. 45. Fig. 50.—Epithelium of ileal folds. A., middle of folds; B., furrow between folds; L., longitudinal muscular bands. 1; S. Entomological Commission Vol. 2 Plate VI Fi£ 45 Fig 43 Fig 44 'Fig 46 F,g48 Fig 47 Fig 49 Fig 50 C S Minot, del. HISTOLOGY OF THE LOCUST. Tc.°* Sinclair A San.lii. rii.ua PLATE VII. Fig. 51.—Transverse section of ileum. L., longitudinal muscular bands; wtuc. C., cir- cular muscular coat; Ep., epithelium. Fig. 52.—Transverse section through the furrow between two ileal folds. F.t furrow; cm., cuticula; Ep., epithelium; conn., connective tissue; tnuc. C., circular muscles. L., longitudinal muscular band. Fig. 53.—Caloptenus spretus. Epithelium of rectal glands. Fig. 54.—-Surface view of the interior of the proventriculus; cV, central; d", molar processes of the teeth; a., longitudinal, interdental ridge. Fig. 55.—Longitudinal section of the wall of the proventriculus. Fig. 56.—Epidermal cells, seen from their outer surface. Fig. 57.—Spiral threads of the same trachea. Fig. 58.—Transverse section of the proventriculus; d', central: d", molar process of the teeth; ep., epithelium; conn., connective tissue; a., longitudinal ridge; C., subdental canal; muc., muscularis. U S. Entomological Commission Vol. 2 Plate VII. F.’4 S' P’S 52 Fi£ 5* R4 S3 FiA 56 Fi! 55 Fig 58 Fi$ 57 (' S. Minot, del. HISTOLOGY OF THE LOCUST. AND CRICKET. Tkns Sinclair it San/lith, Phils. PLATE VIII. Fig. 59.—Cuticula from the lateral portion of one of the middle abdominal segments, to show the nodules b b and hairs. Fig. 60.—Cuticula of the crop. Fig. 61.—Tracheal epithelium, from a large trunk. Fig. 62.—Connective tissue from the ovary. Fig. 63.—Cuticula from the upper and anterior portions of the dorsal arch of one of the middle abdominal segments, h., cuticular hair. Fig. 64.—Ovarian tube. Ch., cord; a-b, region in which the eggs are first formed. Tu., part of the external tunic. In order to draw this part the focus had to be changed. Fig. 65.—Cuticula from the side of the dorsal arch of one of the middle abdomina segments. * Fig. 66.—Wall of the ventricle after removal of the epithelial and glandular cells. U. S. Entomological Commission Vol. 2 Plate VIII S9 Fi£ 60 Fi& 61 >Fi£ 64 Fig S3 HS62 H 65 Fiji 66 ' & fttmoL, del. Ta1s Sinclair <* Son. litii, Pin I a. HISTOLOGY OF ANABRUS.