EARLY HUMAN EMBRYOS AND THE MODE OF THEIR 
PRESERVATION. 
By FRANKLIN P. MALL, 
Professor of Anatomy, the Johns Hopkins University. 
[From The Johns Hopkins Hospital Bulletin, No. 56, December, 1898.] [From The Johns Hopkins Hospital Bulletin, No. 36, December, 1893.] 
EARLY HUMAN EMBRYOS AND THE MODE OF THEIR 
PRESERVATION. 
By FRANKLIN P. MALL, 
Professor of Anatomy, the Johns Hopkins University. 
Nearly all human embryos which come into the possession 
of embryologists are of little value for careful study, because 
they have been preserved carelessly. Of fifty embryos less 
than six weeks old, which have come into the writer’s hands 
during the last few years, only six have proved to be of 
value, and these came from three physicians. In nearly all 
cases the specimen is destroyed by placing the ovum in very 
dilute alcohol, and in so doing it is handled very roughly. 
Poor specimens, however, are better than none at all, there- 
fore in all cases the ova should be preserved, even if there 
be but little hope to obtain a good specimen. The best 
and most convenient method of preserving young embryos is to 
place the unopened ovum, with the least possible handling, in 
a large quantity of very strong alcohol. The alcohol of drug- 
gists is in no case too strong, and, according to my experience, 
is as a rule too weak. Often the ovum is wrapped in a towel 
and then placed in a small quantity of alcohol and water. 
This is an excellent method to preserve museum specimens, 
bilt it practically ruins every embryo for microscopic study. 
When an ovum is placed in, say four ounces of strong alcohol, 
the water of the ovum dilutes the alcohol to a proper strength. 
Those physicians who have the proper opportunities should 
place the specimen as soon as possible, and without opening 
the ovum, in seventy per cent alcohol, i. e., absolute alcohol 
reduced by volume to seventy per cent. At the end of a day 
or two the alcohol is to be renewed, and in this solution the 
specimen may be preserved indefinitely. 
A second convenient method is to place a specimen in quite 
a large quantity of Muller’s fluid, to be changed once or twice 
during the first few days. The embryo is fully hardened in 
about a month, and then it iff for a\ day or j 2 
two, after which it is to be preserved in seventy per cent 
alcohol. 
Ten per cent nitric acid is a convenient and a most excel- 
lent method. The ovum is to be placed in four or six ounces 
of a ten per cent solution, and opened while in the fluid, care 
being taken not to injure the embryo. According to its size 
(if not over an inch long), it should remain in the acid for 
from thirty minutes to two hours. At the end of this time it 
is to be placed in seventy per cent alcohol. 
Another excellent method is to harden the embryo in satu- 
rated aqueous solution of corrosive sublimate. The specimen 
is to be treated as in the ten per cent nitric acid, but it is to 
remain in the sublimate longer. These specimens are then to 
be preserved in seventy per cent alcohol. 
There are many other methods, but if any of the above are 
employed there will be a sufficient supply of material to aid 
the study of human embryology. It is really wonderful to 
see what progress has been made in this study when we con- 
sider how difficult it is to obtain good material. Home of the 
most important discoveries have been made in the careful 
study of a few well-preserved human embryos, as u glance at 
the many papers of His and the excellent text-book of Minot 
will show. 
Specimens of human ova are not only of value and interest 
to the embryologist, but are of great importance to the physi- 
cian in determining the duration of pregnancy. We can easily 
see why it is easier to determine the age of a young ovum 
correctly than to determine the age of the foetus at full 
term; in the former the error must be less than a month in 
order to be overlooked, while in the latter it may exceed this 
time. Furthermore, in the study of young human ova we 
may make comparisons with the embryos of other mammals 
upon which experiment can be made. 
Formerly it was quite generally admitted that the age of 
an embryo is determined by the time of a certain cohabitation. 
In many cases it was attempted to locate the day exactly. 
After it had been shown that the ovum is usually extruded 
from the ovary during menstruation, it was then thought that 
the egg could be fertilized at any point between the ovary and 
the uterus. The time required for the ovum to pass through 3 
the Fallopian tube was considered the time in which it was 
capable of being fertilized. 
Our .most definite information regarding the fertilization of 
the mammalian ovum has been obtained from experiments 
upon the dog, rabbit and guinea-pig. In these animals it is 
found that the spermatozoa pass through the uterus and tubes 
in from twelve to twenty-four hours after copulation, and 
await the ovum in the upper part of the tube. The ovum 
after leaving the ovary enters the tube before it is fertilized 
by the spermatozoon, and usually begins to divide before it 
has reached the middle of the tube. After several days the 
ovum reaches the uterus, and by this time the egg has divided 
into many cells, which now begin to arrange themselves in 
layers to form the blastodermic membranes. 
It is possible that the spermatozoa retain their power to 
fertilize for a very long time, if we can judge by their vitality. 
Piersol* has recently made experiments upon human sperma- 
tozoa and finds that they are motile eight or ten days after 
removal from the body. From this observation it is fair to 
assume, as he does, that within the uterus and Fallopian tubes 
their vitality is still greater. However this may be in man, 
in the lower mammals the arrangement is such that a large 
number of spermatozoa await the ovum in the upper part 
of the tube, and furthermore, coitus in rabbits hastens ovula- 
tion (Coste). 
The evidence from the above observations is that the ova of 
many mammals are fertilized in the upper part of the Fallo- 
pian tube, and there is every reason to believe that the same is 
true in man. Tubal and abdominal pregnancies speak for this; 
in the latter form, the placenta is never attached to the peri- 
toneum but to the mucous membrane of the tube, suggesting 
that the fertilization took place in the beginning of the tube. 
Impregnation is nearly always marked by a cessation of 
menstruation, and it remains to be shown whether or not 
the fertilization takes place during the last menstrual period 
or at the time of the first cessation. The experiments upon 
lower animals show that fertilization of the ovum takes place 
soon after the rupture of the Graafian vesicle, and it is fair to 
assume that the same is true in man. After a Graafian vesicle 
* Piersol: Anatomischer Anzeiger, 1893. 4 
ruptures it is followed by a corpus luteum, but its history is 
by no means as well known as is generally l>elieved. Our 
most trustworthy data have been collected by Leopold,* and 
the more he studied ovaries which had been removed in oper- 
ations the less definite his conclusions became. We must not 
lose sight of the fact that the ovaries he removed were to a 
great extent from women suffering from all kinds of disorders, 
conditions which no doubt may have complicated his results. 
In general his conclusion is that a corpus luteum is found in 
most cases, which from its appearance dates from a menstrual 
period. During the intermenstrual period he frequently found 
in addition to a well-formed corpus luteum, a freshly ruptured 
follicle, indicating that a second and intermenstrual ovula- 
tion had taken place. This seems to indicate that ovulation 
takes place more frequently than menstruation. In other 
cases in which menstrual periods lapsed the women still con- 
tinued to ovulate. This is by no means remarkable, for it is 
known that women often become pregnant before menstrua- 
tion has reappeared during lactation. Also young girls may 
become pregnant without ever having menstruated. 
From all the observations which have been made the con- 
clusion is that in most cases the corpus luteum begins to form 
some time during menstruation, but it is extremely difficult to 
locate the exact date. A few of Leopold’s cases which are 
taken from women just before or during* the first few days of 
menstruation are very important regarding this point. In the 
table the -j- indicates the probable time of ovulation. 
Day of Observa- 
tion after the 
End of Month. 
beginning of Menstruation. 
beginning of 
Menstruation. 
26 
28 
27 
28 
Day 
1st. 
2d. 
3d. 
4th. 
1 
+ 
2 
+ 
3 
+ 
4 
+ 
26 
+ 
* Leopold : Archiv fur Gynaekologie, Bd. xi u. xzi. 5 
In these five cases ovulation took place just before menstru- 
ation, and we hope that the near future may add a great many 
more cases to the table, for the removal of ovaries is by no 
means a rare operation at the present time. 
In spite of our ignorance of the relation of ovulation to 
menstruation, it is quite certain that there must be one, and 
that when it is better known it will be possible for us to deter- 
mine much more accurately the age of embryos and the dura- 
tion of pregnancy than at the present time. The obstetrician 
is too well aware that an error of several weeks is often made, 
and really lays no great stress upon the mistake. This error 
is not very great for a foetus at full term, but is very serious 
when the age of an embryo of the first month is to be deter- 
mined. 
The duration of pregnancy has been studied over and over 
again, and all kinds of views regarding the time of its begin- 
ning have been entertained. In nearly all cases the statistics 
are not complete, and the results are of little value for us to 
determine accurately the beginning of pregnancy. Hasler* 
in his inaugural dissertation has given us trustworthy data of 
twenty-eight cases in which the menstrual period, date of 
cohabitation and the birth of the child are given. In addition 
he gives an extensive discussion of the whole subject in ques- 
tion. I have tabulated twenty-four of his cases from the 
twenty-eight, excluding the other four because the data are 
not complete. In all the cases given the cohabitation did not 
exceed a day, and it is remarkable that in each case the follow- 
ing menstrual period lapsed. The cases were selected by 
Hasler with great care and bear every cross-examination. In 
the table I give the average duration of pregnancy when esti- 
mated from the beginning of the last menstruation, in the 
first column, and when estimated from the day of cohabita- 
tion, in the second column. 
* Hasler: Inaug.-Diss., Ziirich, 1876. 6 
% 
Time of Copulation. 
Number of 
Cases. 
Duration of Pregnancy when 
estimated from 
Boainulnirof last 
Menstruation. 
Day of Copulation. 
First week of menstruation. 
9 
278 days. 
273 
Second “ “ “ 
12 
282 
272 
Third “ “ “ 
0 
No cases. 
No cases. 
Fourth “ “ “ 
3 
299 
209 
The above table contains our most trustworthy cases, and 
is of much value regarding the duration of pregnancy. Many 
other cases are scattered through the literature, and at some 
future date I hope to tabulate most of them. 
Leuckart* has given us data of 110 women, each of whom 
gave birth to a child within ten months after marriage. The 
cases were all taken from a single village, and for this reason 
most of them must be trustworthy. In these cases the 
first cohabitation and the date of the birth of the child are 
given, but unfortunately the date of the last menstruation is 
omitted. When the births are tabulated from the date of 
marriage it is remarkable that the greatest number fall in the 
40th and 42d weeks. Stated more accurately, the greatest 
number fall on the 276th and the 295th days after marriage. 
I.euckart believed that these two maxima in the number of 
births represented the last ovulation before, and the first ovu- 
lation after marriage. The 276 days would then represent 
about 286 days, and the 295 about 285 days. 
If we take the three sets of experiments by I>?opold, Hasler 
and Leuckhart we can make them harmonize if we admit that 
ovulation can take place at any time; it seems as a rule to take 
place during and immediately after menstruation, and often 
just before the period. Considering the Graafian vesicle, which 
is gradually becoming larger and larger, it is fair to assume 
•Leuckart: Wagner’s Handworterbuch der Physiologie, Bd. 4. 7 
that its thin wall which is to be ruptured by the hyperaemia 
of menstruation, can also be ruptured by undue excitement 
during the intermenstrual period. This is suggested to us in 
Hasler’s cases in which there was but a single cohabitation in 
unmarried women. The idea is strengthened by Leopold’s 
study of the corpus luteum, and by the fact that coitus hastens 
ovulation in lower animals. 
From the above statement it is quite evident that our infor- 
mation regarding the rupture of the Graafian vesicle, its rela- 
tion to menstruation and to fertilization of the ovum, needs a 
most thorough revision. . This cannot possibly be done by one 
individual alone, and I therefore ask the cooperation of 
physicians. Each can contribute his part. 
Up to the present date our most valuable information 
regarding the probable time of the fertilization of the ovum 
has been obtained from the study of a few young human 
embryos. An error of a few days or weeks would hardly be 
noticed in a foetus at full term, but in an embryo two weeks 
old the same error becomes a matter of great importance. 
This error has induced embryologists to study the statistics 
of the obstetricians most carefully. 
In order to locate the ovulation from which to compute the 
age of an embryo, I have tabulated all the young embryos 
which have been published with a full history. Numbers 2, 3, 
4, 6 and 7 are not as complete as they might be, but they are 
of great value because they fill important gaps. In No. 2 the 
time between the last menstrual period and the abortion is 
given roughly as five weeks. Still it is fair to assume that the 
time must have been between 30 and 40 days. In Nos. 3 and 
4 the size of the embryo is not given, hut in both cases the 
ovum is so small that the embryos could not have been over 
two millimeters long. 
From a comparative standpoint we can easily determine the 
age of human embryos within four weeks. Counting from the 
last menstrual period, it is very easy to see by the size of the 
embryo whether or not it is, say three or seven weeks old. 
The table shows that, by counting in this way, embryos of the 
same size may differ four weeks in age (see Nos. 6, 14, 16 and 
17). In these cases the ages correspond to those of the other 
cases, if from their time twenty-eight days are subtracted. Number. 
Observer. 
Length of 
embryo 
lu rallli- 
Ulfl ICS. 
Beginning of last 
period. 
Last possible 
cohabitation. 
Time of tlrst lapsed 
period. 
Day of abortion. 
Time between abortion 
and 
Probable age 
of embryo. 
Number. 
Last period. 
First lapsed 
period. 
] 
Mall 
4 
January 25. 
February 22. 
i 
J* 
1.54 
(?) 
7 " (?) 
2 
8 
Early November. 
42 days. 
14 44 
14 44 
3 
4 
X -4- 28. 
X 4- 38. 
38 •* 
10 44 
10 44 
4 
5 
2.1 
x 
X + 28. 
X 4- 42. 
42 ** 
14 “* 
14 44 
5* 
fra 
Mall 
8.1 
December 5. 
41 44 
13 44 
13 44 
5 
• 
2 5 
May 19. (?) 
14 “ 
14 44 
6 
7 
Ilia (HR) 
2 8 
October 14 15 
60 “ (?) 
14 •• (?) 
14 44 
7 
8 
ilia '(I* ) 
2.15 
40 “ ' 
12 44 
12 44 
8 
• 
10 
Graf Spee 
260 
8.0 
X 
X + 28. 
X + 42. 
42 44 
43 “ 
14 44 
15 44 
14 44 (?l 
15 44 
9 
10 
11 
His (ini.) 
8.2 
March 26. 
April 4.* 
April 23. 
Mav 13-16. 
48 “ 
20 44 
20 44 
11 
It 
Ki'knr 
4. 
45 “ 
17 44 
17 44 
12 
18 
u 
May 8. 
52 ** 
24 44 
24 44 
13 
14 
4.5 
X 4- 20. 
20 44 
30 44 
14 
1ft 
H la~(a) 
4.0 
November 1. 
51 *• 
23 44 
23 44 
15 
ID 
Hin(\V) 
ft.O 
21 “ 
21 44 
16 
4Ji 
x 4* 21* 
21 “ 
21 ** 
17 
18 
Stubenrauoh (I) 
6.0 
July 1. 
July 8. 
July 28. 
August 14. 
45 “ 
17 44 
17 44 
18 
IV) 
Stubenrauoh ill) 
7.0 
April 1. 
April 14. 
April 28. 
May 20. 
51 ** 
22 44 
22 44 
19 
•JO 
Mall 
7.0 
52 ** 
24 44 
24 44 
20 
21 
HU (Stt.) 
7.75 
July 5-8. 
July 90.* 
August 3-5. 
September 1-3. 
67 44 
2j, .. 
28 44 
21 
JM 
Koker 
10.0 
April 4. 
April 15. 
May 2. 
June 3. 
60 44 
32 44 
32 44 
22 
S3 
His (Hr.) 
11.0 
April 24 
May 22. 
61 44 
33 44 
33 44 
23 
24 
HU (Hr,) 
18.6 
October 30. 
End of October.* 
November 17. 
December 22. 
63 44 
35 44 
35 44 
24 
25 
His (V ,) 
13.0 
64 44 
36 44 
36 “ 
25 
2D 
Hia (l.ha) 
IT. 
May^ 
51 44 
51 44 
26 
27 
22. 
53 44 
53 44 
27 
88 
Hid 
March 21. 
56 44 
56 4* 
28 
2V» 
Mail 
33. 
X + 28. 
v'l 77 
77 44 
51 44 
51 44 
29 
80 
Minot. 
82. 
January 4. 
February 1- 
March 13. 
68 44 
68 44 
30 
* Earliest cohabitation. 
1. Mall: Anatomiachcr Anaeiger, 1883, p. 630. — 2. Qraf Spee: V ere In Schlesw. Holst. Aerate, Heft II, Sttlck 10; His und Braune's Archiv, 1880, p. 159. 
3. Kelehert: Abhandl. d. KOnlgl. Akad. d. Wiascnschaften su lierlin. 1873, No. 1.—4. Breuss: Wiener med. Wochenschrift, 1877, p. 502.—5. Thomson: Edinburgh 
Medical and Surgical Journal, 1838, p. 139; and Ills: A. m. E„ I, p. 152.—6. Thomson: Edinburgh Medical and Surgical Journal, 1839. p. 139; and His: A. m. E . I, 
p. 15*.—7. His (S. R.) : A. m. B.. I, p 140.—8. His (Lg.': A. m. B„ II. pp. 7 and 74.-9. Qraf 8pee: Verein Schlesw. Holst. Aerate, Heft 11. St&ck 8, 1887.—10. Jantaik : 
Arch. f. mik. Anat., Bd. 30. pp. 560, Ml.—11. His (BB): A. m. B.. II. pp. 7, 74.—12. Bcker: His u. Braune's Archiv, 1880, p. 403.—13. Stubenrauch : Inaug. Diss., Mfln- 
chen, 1889.—14. Wagner: MtUler's Archiv, 1835. p. 373.—15. His (a): A. m. B., I, p. 100.—13. His (Wi: A. m. B., II, pp. 7 and 74.—17. Hensen: His u. Braune's 
Archiv, 1877, p. 1.—18. Stubenrauch: Inaug. Dias., MQnchen, 1889—19. Stubenrauch: Inaug. Diss.. MOnchen, 1889.—20. Mall: Journal of Morphology, Vol. 5, p. 459. 
—SI. His (Stt.): A. m. B„ II. pp. 8 and 74.-22. Bcker: loon. Ph.vsiol. XXVIII, p. 11.—23. His (Br,); A. m. B., II, pp. 8 and 74.-24. His (Brt): A. m. B.. II. pp. 9 and 74. 
—23. HlstM,): A. m. E , II, pp. 9 and 74 —36. His tLha.): Am. E.. Ill, p. 238—27. Minot: Human Embryology, p. 392.-28. His: A. m. E., Ill, p. 239.-29. Mall: Not 
published.-SO. Minot: Human Embryology, p. 398.-5*. Embryo from Dr. Bills, of Elkton. Md. 
TABLE OF YOUNG EMBRYOS. 9 
This seems to indicate that, as a rule, fertilization of the ovum 
takes place during the ovulation which precedes the first men- 
struation which has lapsed. After Reichert had shown that 
menstruation is only a method of clearing out the uterus after 
an ovulation, and after Leopold had shown that the mucous 
membrane of the uterus undergoes histological changes before 
ovulation, it is fair to assume that the latter changes are only 
preparatory to the reception of the ovum, and that when the 
unfertilized ovum reaches the uterus, menstruation is only a 
method of reducing the uterus to its former condition. 
It is necessary to compute the age of the embryo from the 
last menstrual period in only eight of the cases, and it is 
not probable that just these eight embryos have grown too 
rapidly. All the rest must have twenty-eight days subtracted 
from the time in order to make them correspond with the 
above eight. These are the main reasons for assuming that 
the fertilization of the egg takes place just before the first 
menstrual period which lapsed. It may be that a great many 
fertilizations take place during the last menstrual period, but 
that when menstruation has once begun, the activity of the 
uterus destroys the ovum, and that, as a rule, only those are 
preserved in which menstruation does not follow the last ovu- 
lation. At least the embryological evidence indicates that 
fertilization takes place just before the first lapsed period, and 
at present embryologists make their specimens correspond to 
one another by reckoning the ages of most embryos from the 
last menstrual period minus twenty-eight days. 
The table shows, in addition, that in certain pregnancies the 
first cohabitation followed the last menstrual period. It can- 
not be that in these cases the ovum of the last period could 
have been fertilized, for it is quite certain the ovum loses its 
power of being fertilized shortly after it leaves the Graafian 
vesicle. 
In case No. 11 (B B), the first cohabitation of a newly mar- 
ried woman took place on April 4, say about five days after 
the last menstrual period; and the woman ceased menstruating 
at once, probably on account of the fertilization of the ovum 
which preceded the first lapsed period. If all the cases of 
newly married women in which there was an early pregnancy 
were collected it would, no doubt, be shown that in many of 10 
the cases the women did not menstruate at all after marriage. 
All of Hasler’s cases of single cohabitation speak for this. 
In several of the cases given in the table, the last cohabita- 
tion took place several weeks before the cessation of menstru- 
ation, showing that the vitality of the spermatozoa within the 
female organs lasts for at least a few weeks, or that the last 
cohabitation was accompanied by an ovulation. 
Enough specimens of human ova have been studied and 
compared with those of lower animals to render it very easy to 
determine the age of the human from comparative standpoint 
alone. Thus, for instance, the guinea-pig of two weeks is 
about as large as the rabbit of the same age. These again are 
about as large as a dog of three weeks, and all three are of the 
same stage of development as a human embryo of three and 
one-half weeks. Then the history of some of the animals 
closely related to man is now quite well known, and from com- 
parative embryology we can conclude with great certainty 
whether or not a given ovum is three or four weeks old. In 
addition to this we have the above table, which cannot be im- 
proved much by adding or subtracting a few days from the 
ages of some of the embryos, as the error cannot be over three 
days. Therefore we believe that in many cases fertilization 
of the ovum must take place in the neighborhood of, and 
usually before some menstrual period. We cannot deny, how- 
ever, that there may be a difference between the relation of the 
beginningof pregnancy to menstruation, in first cohabitations, 
and those which follow later on ; in the first, ovulation should 
be irregular, in the second cases, as regular as it is independ- 
ently of copulation. 
In conclusion, I add a brief history and description of a few 
young human embryos, and I begin with the youngest which 
has as yet been cut into serial sections for microscopic study. 
To be sure, many very young human ova have been seen and 
the outer forms studied, and the best known of these is Reich- 
ert's,* a picture of which is seen in every text-book. Even 
such a small thing as an unfertilized human ovum has been 
found in the Fallopian tube,f showing that with industry and 
•Reichert: Abhandl. d. Konigl. Akad. d. Wins., Berlin, 1873. 
f Hyrtl: Zeit. f. rat. Med., N. F., IV. 11 
patience “a needle may be found in a haystack.” I am 
under obligations to Dr. Kittredge, of Nashua, New Hamp- 
shire, for the above-mentioned specimen. It was quite well 
preserved when it came into my hands, as it had been placed 
in a large quantity of sixty per cent alcohol several hours 
after the abortion. Dr. Kittredge most carefully obtained 
the history for me, which has borne the most rigid cross- 
examination in every respect. 
“ The woman from whom the specimen was obtained is 25 
years old, menstruates regularly every four weeks, the periods 
lasting from four to five days. She gave birth to a child Sep- 
tember 19, 1892, and had the first recurrence of menstruation 
December 19. The second period followed on January 25 and 
was very profuse; it lasted until February 1. The next period 
should have begun about February 22, but on account of its 
lapsing the patient concluded that she was pregnant and 
called at my office a few days later. I did not examine her, but 
asked her to remain quiet and await developments, as I 
thought possible that she might be pregnant. On the evening 
of March 1 she fell and sprained herself, and during the same 
night had a scanty flow. The flow recurred each day, and on 
the seventh of March she passed the ovum. It was kept in a 
cool moist cloth for twenty hours, and when it came into my 
hands was at once placed in a large quantity of 60 per cent 
alcohol.” * 
The ovum is quite large for its age, having a long diameter 
of 10 mm. and a short diameter of 7 mm. It is covered with 
villi only around its greatest circumference, having two spots 
without villi, as was the case with Reichert’s ovum. The villi 
of the chorion are from 0.5 to 0.7 mm. long and are branched. 
Upon opening the chorion it was found that the germinal 
vesicle was situated just opposite the border of the zone of 
villi. There was much coagulated albumen around it, which I 
did not remove and therefore could not obtain good camera 
drawings. The portion of the chorion to which the vesicle was 
attached was cut out and stained with alum cochineal and 
cleared in oil, but even after this treatment it was impossible 
to obtain any clear picture. The specimen was next imbedded 
* Letter from Dr. Kittredge, April 27, 1893. 12 
in paraffin and cut into sections 10 /i thick. The series proved 
to be perfect From the sections a reconstruction was made 
in wax, and the accompanying figure (Fig. 1) is a sagittal 
section of it. 
Fio. 1—Sagittal section of the Klttredge embryo. Taken from 
the reconstruction. Enlarged 33 times. Ch, chorion; AL, allan- 
tois ; X, position of embryo; r, blood-vessels. 
The sections and reconstruction show that the embryonic 
vesicle is attached to the chorion by means of a stem (Bauch- 
stiet). The vesicle itself is composed of two layers, between 
which, at a distance from the stem, there are indications of 
blood-vessels or a middle embryonic layer. In the immediate 
neighborhood of the attachment of the vesicle to its stem 
there is a deep and short invagination of both layers of the 
vesicle. At first it was somewhat difficult for me to interpret 
the meaning of the specimen, because there is as yet no decided 
mark of the embryonic body. The location of the allantois 13 
does, however, give us some clue to the future position of the 
embryo. It is somewhat complicated on account of the yolk 
cavity extending into the stem, but I do not think this is 
serious. I think there is but one rational interpretation of the 
Fig. 2.—Sagittal section of Graf Spee’s embryo. Ch, chorion; AM, amnion ; 
AL, allantois; A, amniotic cavity; Y, yolk cavity or umbilical vesicle; NC, neur- 
enteric canal; X, embryo: v, blood-vessels. 
specimen, i. e., it is an apparent inversion of the membranes, 
as is the case in many of the rodents. The invagination is the 
cavity of the amnion. It is comparatively easy for us to 
imagine how this embryo may he changed into one a little 
older, as for instance that described by Graf Spee. After the 
opening of the invagination closes, the walls a and a approach 
each other and the layers b and b move down on either side of 
the invagination. Then the neurenteric canal breaks through. 
This is practically the state of things as we find them in Graf 
Spee’s embryo. 14 
The accompanying figure (Fig. 2) ie from a sketch by Graf 
Spee,* which he has kindly permitted me to publish. His 
original publicationf does not give the above picture, which is 
of such great importance in the study of young embryos, and 
for this reason I add it. As the figure shows, the yolk-sac 
occupies nearly the whole length of the embryo, and is not 
much larger than the amniotic cavity. The embryonic medul- 
lary plate, X, projects slightly forward to form the head-end of 
the embryo; it is a broad thickened layer of ectoderm, and 
seen from above is slightly constricted in its middle. Towards 
the tail-end of the embryo in the middle line there is a com- 
munication between the amniotic and yolk cavities, the 
neurenteric canal; behind this there is a primitive streak. 
The neurenteric canal or blastopore is the very interesting 
part in this embryo, because it is the only instance in human 
embryology in which this canal has been seen. There are 
many other parts which have been carefully studied in this 
specimen, but the few mentioned are sufficient to show the 
great value of it 
When the sagittal sections of the Spee embryo are placed 
beside that from Dr. Kittredge, we at once obtain suggestions 
regarding the early formation of the amnion, allantois and 
yolk vesicle. These parts are by no means formed in the same 
way in different animals, and up to the present we have had 
to content ourselves with a theory by His, which has been 
extensively copied in the various embryologies. 
I have drawn the parts I consider homologous with the 
same kind of lines. A little imagination, aided by some 
recent work by SelenkaJ on higher mammals is my reason 
for believing that the invagination in Fig. 1 is converted into 
the amniotic cavity of Fig. 2. 
After the second week a great number of human embryos 
have been obtained, many of which have been studied carefully 
by embryologists, especially Professor His. To give an idea 
of the growth of the external form of embryos, I add a figure 
taken from His’s Atlas.§ The ages of the embryos selected 
• Letter from Graf Spee, April 9, 1893. 
fGraf Spee: His u. Braune’s Archiv, 1889. 
$ Selenka: Stadien, Taf. 41, Fig. 6. 
$His: Anatomie mensch. Kmbryonen. Leipzig, 1880. 15 
Fig. 3.—Six human embryos taken from His’s Standard Chart. Enlarged 5 
times. The figures in the cut indicate the age of the embryo in weeks. 2 is 
His's embryo SR; 3, embryo Lr; 4, embryo A ; 5, embryo Cn; 6X, embryo 
XCI; 8, embryo Wt. 16 
represent from two weeks up to the beginning of the third 
month. The embryo from which the smallest figure is taken 
is slightly larger and older than Graf Spec’s embryo, and a 
week later (3) the form of the body is already outlined. 
During the fourth week the eye, ear, branchial arches and 
extremities appear, and in the sixth the leg, foot and toes are 
quite well formed. 
The general conclusions formulated by Professor His to 
determine the age of human embryos are, when slightly modi- 
fied, as follows: 
1. The beginning of development is the time of impregna- 
tion, t. e., at that moment when the spermatozoon enters the 
ovum. 
2. The time the egg leaves the ovary is marked by menstru- 
ation, but it is not necessary for the Graafian vesicle to rup- 
ture during menstruation; it may take place immediately 
before, during, or after the hemorrhage. 
3. The egg is not capable of being fertilized at any 
point from the ovary to the uterus, but only shortly after 
it has left the ovary; as a rule, as it is entering the Fallopian 
tube. 
4. The spermatozoa which have entered the female sexual 
organs must await the ovum in the upper part of the Fallopian 
tube, and can retain their vitality here several days, or possi- 
bly several weeks. The time of cohabitation is, therefore, not 
directly related to the age of the embryo. 
5. The age of many embryos is to be estimated from the 
beginning of the first menstrual period which has lapsed, 
although it is possible to have a menstruation after fertiliza- 
tion of the ovum. 
6. The age of an embryo can be expressed by the following 
formulas: A — X— Mor A — X—M— 28, in which A”is the 
date of the abortion and M the beginning of the last period. 
The second formula is for cases in which it is necessary to 
count from the first lapsed period. 
There is no reason why the gynecologist should not add his 
share in determining the age af embryos. Any physician can 
add greatly to the subject if he will record all cases in his 
practice after the plan of Dr. Kittredge’s letter. It is not 
necessary for him to confine himself to young embryos alone, 17 
but be might also include foetuses at full term; especially 
those of newly married women will be valuable. Moreover, if 
the young specimens are carefully preserved, he will do a great 
work hand in hand with the embryologist. 
To facilitate the arrangement of data which may be 
obtained, I append two tables with a single case in each. 
The History of an Embryo. 
o 
a 
Reginning of last 
H- 
menstrual period. 
a 
h* 
Duration of 
P 
period. 
on 
to 
Frequency of 
P 
periods. 
CD 
Date of abortion. 
tO 
o9 
■= c 
i B 
(t a 
Po 
Dimensions of 
embryo. 
e+ 
S'* 
a & 
P 
Hi® 
50 
CD 
CD **. 
* B 
B 
P 
** 
g* 
O O 
*1 o 
2.cr 
o o 
P 03 
History of a Child Born within Ten Months after Marriage. 
« 
Beginning of last 
o 
period before 
marriage. 
o 
Or 
P* 
Duration of 
period. 
CD 
8 
a 
Frequency of 
p 
periods. 
CO 
Ch 
Date of marriage. 
I-1 
£ 
Dates of periods 
•w 
after marriage. 
-i 
CO 
a. 
Duration of last 
period. 
00 
O 
© 
Date of birth of 
e*- 
child. 
-1 
tc 
W 
fv^ 
1 
i5 •< 
® ® 
►» 
'i 
P 
•1 
CD 
If there is more than one period after marriage, the date and dui-ation of 
each should be given.