Paper - Age of human embryos (1901)

From Embryology

Mall FP. Age of human embryos. (1901) Ref. Handb. Med. Sci. 2d ed. 3: 794-797.

Mall FP. Human embryos pathological. (1901) Ref. Handb. Med. Sci. 2d ed. 3: 797-.

Age of Human Embryos

Introduction

It has been quite generally accepted that the age of an embryo must be determined by the time of a certain cohabitation. In many cases it was attempted to locate the day exactly. After it had been sliown that the ovum is extruded from the ovary at or before menstruation begins, it was then generally admitted that the egg could be fertilized at any point between the ovary and the viterus. the time required for the ovum to pass through the Fallopian tul)e was considered the time in which it was capalde of be ing fertihzed. According to the above, these conclusions are not based on a sound footing, because of the difficulty in obtaining accurate observations, and also because they do not agree with the results olitained from the lower animals. Both Coste and His have sliown that the eggs of the hen are fertilized ten or more days after copulation, and the former has shown that the egg is no longer capable of fertilization after it has passed through the lower portion of the oviduct.


Impregnation is nearly always marked by a cessation of menstruation, and it now remains to be shown whether the fertilization takes place during the last menstrual period, or at the time of the first cessation ; for it is known from the examination of the ovary in the living subject that ovulation usually comes ju.st before menstruation. Since it seems to be necessarj' to fertilize the egg just as it leaves the ovary, it is probable that impregnation takes place just before the mcn.strual period. To locate the menstrual period, from which to compute the age of an embr3'0, we must consult the tables, which are in part copied from His.


From a comparative standpoint we can easily determine the age of human embryos within four weeks. Counting from the last menstrual period, it is quite 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 have a difference of four weeks in age (see Table II. , 3, and Table III. , 8, 10 and 14) . In these cases the age corresponds to the other cases, if from their time twentyeiglit days are subtracted. This already iudicates that, as a rule, fertilization of the ovum takes place during the ovulation wliicli precedes the first menstruation wliieli has lapsed. After Reicbert liad sliown that menstruation is only a method of eli'aring out flie uti'rus after an ovulation, and after Leoi)old had .shown lliat the mucous membrane of the uterus undergoc^s histological changes before ovulation, it is fair to assume tliat the latter changes are only preparatory to the reception of the ovum, and that when the unfertilizrd ovum reaches the uterus, menstruation is only a method of reducing the uterus to its former condition.


Only in four of the cases is it necessary to compute the age of the embryo from the last meustrual period, and it is not fair to assume that just these four embryos have grown too rapidly. All the rest must have twenty eight days subtracted from their time in order to make them correspond with the above four. These are the main reasons for assuming that the fertilization of the egg takes place just before the first menstrual period which has lapsed. It may be that a great many fertilizations take place during the last menstrual period, but tliat when menstruation has once begun, the activity of the uterus destroys the ovum, and that, as a rule, only tlio.se ova are preserved in which menstruation does not follow the last ovulation. At least the embryological evidence speaks for this, and at present embryologists make their specimens correspond with one another when they reckon their ages from the last menstrual period, minus twenty-eight days.


The tables show, in addition, that in certain pregnancies the first cohabitation followed the last menstrual period. It cannot be that in these cases the ovum of the last period could have been fertilized, for it is quite certain the ovum loses its jxjwer of l)eing fertilized shortly after it leaves the Graafian follicle. In the case given in Table III., 1 (B B), the first cohabitarion of a newly married woman took place on April 4th, say about five days after the last menstrual period; and the woman ceased menstruating at once, prol)ably on account of the fertilization of the ovum of the following ovulation. 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 the cases the women did not menstruate at all after marriage. At present, however, I know of four such cases. His has tabulated cases given 1)y Ilasler, in which the tirst copulation, the last menstrual peiiod, and the date of birth of the child are given. In all of these cases the age of the fa>tus is from two hundred and seventy to two hundred and eighty days, if the beginning of pregnancy is reckoned from the beginning of the first period which has lapsed. If the beginning of pregnancy is placed at the first cohabitation, the age of the foetuses varies fully a month according to the time of the cohabitation; if the time which has elapsed between the cohabitation and the first menstruation which lapsed is subtracted from the duration of the pregnancy, then the lengths of the pregnancies are practically alike. Assuming that the lengths of pregnancies should be about the same, it makes it highly probable that fertilization takes place at the time of the first menstrual period which has lapsed rather than at the time of cohabitation.


In several of the cases given in the tables, the last cohabitation took place several weeks before the cessation of menstruation, showing that the vitality of the spermatozoa within the female organs lasts for at least a few weeks. It is probable, however, that the spermatozoa cannot live in the Fallopian tubes or uterus for over a month, because authentic posthumous births alway's take place within two hundred and eighty-day's after the father's death.

The general conclusions formulated by Professor His, and accepted by embryologists. are as follows:

  1. The beginning of development is the time of impregnation, i.e., at that moment when the spermatozoon enters the ovum.
  2. The time the egg leaves the ovary is marked by menstruation, l>ul it is not necessary for the Graafian vesicle to rupture during menstruation ; it may take l)lace two (u- three days before or even during the hemorrhage.
  3. The egg is not capable of being fertilized at any ]ioint from the ovary to the uterus, but only shortly after it has left the ovary; as a rule, as it is entering the Fallo|iian tulie.
  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 ]iossibly several weeks. The time of cohabitation is, therefore, not directly related to the age of the embryo.
  5. The age of the embryo is to be estimated from the beginning of the first menstrual period which has lapsed, although it is possililc to have a menstruation after fertilization of the ovum.
  6. The iige of au embryo can be expressed by the following fornmhi : A = X - M or A = X-M - 28, in wliicli X is the date of the abortion and M the beginning of the last period. the second forniuUi is lor embiyos in wbich it is necessary to estimate the age by ciuinting from tbe first lapsed period.

Preservation

The human embryos which come into the bands of the embryologists are nearly altogether worthless for careful study, due to careless preservation. Of one-hundred and fifty embryos less than six weeks old, which have come into the writer's hands during the past few years, only a few have proved to be valuable, and these came from two physicians. The main reason why specimens are destroyed, in nearly all ca.ses, is that the ovum is placed in very dilute alcohol, and in so doing it is also handled very roughly. Yet poor specimens are better than none at all, and in all cases all ova should be preseived, even if there is but litlle hope for a good specimen. Not only shoiild ova which appear I o be normal be preserved, but all specimens, for lieiiuently pathology


Table I.— Embryos of the Second Week.

Observer.


Peters... Ereuss . . Reicheit.


Siegenbeek van Heukelom.

Gl-af Spee

No. XL*

Keibel

Eteriiod

Graf Spee


A\>


Length of embryo.


0.:l'*5 mill. O.oT mill. 0.8 iiiiLj. 1.0 nun, l.:i mm. l..">4 mm.


0.79 mm. 1.14 :< 1


Dimensions of nnibiiical \'esicle.


0.10 iiini..


1.08 < 1 mm . 1.5 X 1 mm .

I.s X 1.5 nun


Itimoiisions of


o.ii ■. 1.5 / 1.5 mm.

5.0 mm

5.5 .< 'riM mm


5.5 X 4.5 mm

7.(1 X 5.5 mm

lO.OX 7.0 X I.Oram.

8.5 X 7.75 X 6 mm . . 10.x X 8.2 X 6 mm . . 10.0 X 8.5 X ti.5 mm .


IJ 'IJ fH _ 3

-1 'U oj "5 ■


so 1 1 ays.

iS (lays. 42 days.


5 \yeeks. 41 days. .


34 days. . 5 weeks.


Probable age.


10 days., 14 days..


12 dayst.

13 days. .

12 days +.

References, or from wbom obtained.


Einhettungdes mensch. Eies. 1899. Wiener tned. Wochenblatt, 1877. Abhandl. d. k. A. d. Wiss., Berlin,

1873. His' Arrhiv, 1898. His' Arrhiv, IS'.lii. Dr. Kittri'dgp, Nashua, N. H. His' Ariliiv, Ls'.iO. Anat. Anz., .xv.. 1898. His' Ardiiv, 1890.


The Roman numbers refer to the embryos in my colleetion.

t Twelve days in my estimation, as Graf Spee only in a general way gives live weeks as the time between the last period and the abortion.


Table II. — Embryos of the First Half of the Third Week.


5 2i


Observer.


Length

of embryo.


Dimensions of umbilieal vesicle.


Dimensions of ovum.


Time between last period

and abortion.


Probable

age.


References, or from whom obtained.


1

2.1 mm. 2.1 mm.

2.1 mm. 2.12 mm. 2.15 mm.

2.2 mm. 2.2 mm.

2.4 mm.

2.5 mm. 2.0 mm.

2.6 mm. 2.69 mm. 3.0 mm. 3.0 mm.


1.5 X 1 -, 1 mm

2.6 mm

2.3 X 1.8 mm

3.0 X 2.5 X 1.75 mm..

1.6 X 1.2 mm

1.9 X 1.5 mm

2 1X17 mm


IH.O X 18 >;8


41 days. .

42 days..


13 days..

14 days..


Dr. Ellis, Elkton, Md.

5.7 mm


Edin. Med. and Surg. Journal, 1839.


3 4 5 6

7 8 9

10 11 12 13 14


His (E )


8.5 X 5.5 mm


Anat. mensch. Embryonen.

16.3 mm

Anat. Anz., XV., 1898.


His (Lg.)


15.0 X 12.5 mm .... 9.0 X 8 mm


4(1 days. .


12 days..


Anat. mensch. Embryonen. Anat. mensch. Embryonen.


Anat. mensch. Embryonen,


9.0 X 8 mm

Anat. mensch. Embryonen.

2.1 mm


15.0 X 10 mm

15.0 X 12 X 8 mm ..


14 days..


14 days..


Edin. Med. and Snrg. Journal, 1839.

1.9 X 1.8 X 1.6 mm...

2.6X1.7 mm

2.5 X 1.5 mm


Arch, Ital. de. Biol., 12.



8.0 X 7.5 mm

Anat. mensch. Embryonen.



15.0 X 14 mm


42 days..

42 days. .

43 days..


14 days. .

14 days..

15 days. .


Verein. Schles.-Holst. Aerzte, 1887.


His (E.B.)

Janusilf


His' Arch., 1898, p. .58.

A. f. m. A., 30.


2.41 mm.


2.22 X 1.6 X 1.45min.


11.7 X 10.6 ••: 8 mm.

14 days.



Table III. — Embryos op the Second Half of the Third Week.


B


Observer.


Length

of embryo.


Dimensions of umbilical vesicle.


Dimensions of ovum.


Time betw-een last period

and abortion.


Probable

age.


References, or from whom obtained.



His (B. B.)


3.2 mm. 4.0 mm. 4.0 mm. 4.0 mm.

4.2 mm.

4.3 mm. 4.3 mm. 4.5 mm. 4.5 mm. 4.5 mm. 4.5 mm. 5.0 mm. 5.0 mm. 5.0 mm. 5.0 mm. 5.25 mm. 5.5 mm. 6.0 mm. 6.0 mm.



14 X 11 mm

24 X 16 X 9 mm —

'■M'X ifi'mm. '.'.'.'. ...

15 mm


48 days.. 42 days. . 45 days..

51 days . .

52 days. . 38 days. .

20 days..

21 days..

21 days. . IS days. .

45 days..


20 days . . 14 days . .

17 days. .

23 days..

24 days . . 2(j days..

21 days . .

21 days!!

18 days . .

'iV days!!


Anat. mensch. Embryonen.


1

2 3 4 5



Dr. Cole, Peru, 111.

His" Archiv, 1880.

Anat. mensch. Embryonen.

Anat. mensch. Embryonen.

Inaug. Dis., Miinchen, 1889.


Ecker

His (III.)

His (Lr.)

Stubenrauch (K.)

No. OXLVIII

Wagner

No. I

Henseii

No. LXXVI

No. LXXX

His(D2)

His (W.)

His (R.)

Meyer

No. XIX

No. XVI

Stubenrauch (I.)


3.0 X 2.7 mm

2.8 X 2.3 ram


6

7

8

9

10

11

12

13

14

15

16

17

18

19


3 mm

4 mm

4 mm

4 ram

2.5 X 2 x2nim


17 X 14 X 10mm... 'ii x'sd'mm

'22x'2(i'mm

24 X 18 X 8mm.... 2f) X 15 mm

25 X 20 mm

22 mm

22 mm

18 X 14 mm

24 X 18 mm


Dr. Hoeu, Baltimore.

Midler's Archiv, 1835.

Dr. Gavin, Baltimore.

His' Archiv, 1877.

Dr. Mitchell, Chicago.

Dr. Branham, Baltimore.

Anat. mensch. Embryonen.

Anat. mensch. Embryonen, pp. 7, 74.

Anat. mensch. Embryonen.

A. f. m. A., 36.

Dr. Williams, Baltimore.

Dr. Sherwood, Baltimore.

Inaug. Dis., Miinchen, 1889.



Average


4.67 mm.


3.3 X 2.2 X 2 mm . . . . ; 22 X 18 X 9 mm . . .



19 5 days.


Table IV. — Embryos of the Fourth Week.


%

g

•A


Observer.


Length

ot embryo.


Dimensions of umbilieal vesicle.


Dimensions of ovum.


Time between last period

and abortion.


Probable age.


References, or from whom obtained.


1 2

3

4

■, 6


No. CXVI

No. 11

Stuhenramii (11.)


. ().;-( iiini.

. 7.0 mm.

. 7.0 mm.

7 mm


'7.'o"x 4..'i X 4.5 mm . .


38X20X10 mm... 25 X 35 mm


55 days . . .53 days . . 51 days. .


37 days. . 34 days . . 33 days. .


Dr. Ryan, Springfield, 111. Dr 0.0. Miller, Baltimore. Inauff. Dis., Munchen, 1HH9.



18 X 18 mm


Dr. Douglas, Nashville, Tenii.


His (B.)

His (Stt.)


. 7.0 ndn. . 7.75 mm.


4 mm


25 X 33 mm

31 X 17 mm

20 ■' 13 mm


57 days. .


37 days..


Anat. mensfh. Embryonen. Anat. mensch. Embryonen, 8, 74. Anat. menseh. Embryonen.


s


Meyer


. H.O mm.


5 mm


45 mm


3H days..


38 days..


A. f. m. A., 3fi.


"


Average


. 7.34 mm.


5.3 X 4.5 X 4.5 mm. . .


36 X 19 X 10 mm. . .



20 days.



Table V. — Embryos of the Fifth Week.


s

2;


(Jbserver.


Length

ot embryo.


Dimensions ol umbilical vesicle.


Dimensions of ovum.


Time between last period

and abortion.


Probable age.


References, or from whom obtained.


1

o



10.0 mm. 10.0 mm. 10.3 mm. 11.0 mm. 11.0mm. 11.0 mm. 11.5 mm. 13.5 mm. 13.Smm. 13.0 mm. 13.0 mm. 13.0 mm.




80 days. .


32 days..


Icon. Physiol., 28. Dr. Brumm, Detroit. Anat. mensch. Embryonen. Dr. Gushing, Baltimore. Anat. mensch. Embryonen. Anat. mensch. Embryonen. Anat. mensch. Embryonen. Anat. mensch. Embryonen. Anat. mensch. Embryonen. Dr. C. 0. Miller. Baltimore. Anat. mensch. Embryonen. Anat. mensch. Embryonen, 9,



No T.YXYVni



30 X 28 X 15 mm . .



3 4


35 X 35 mm

No CIX

30 X 30 mm


5.0 X 4.5 mm


30 X 37 mm

30 X 35 mm


61 days. .


33 days..



6


His (\('Vn 1



His rUff 1


5.5 X 4.5 mm

6 0X5 mm . ...


30 X 37 mm


8


His (SI.)

His {W\ )


30 X 27 mm



5.0 X 4.5


40 X 32 mm


No. XXXV

His CM 2)



37 days.. 04 days.. 03 days. .


37 days. . 36 days.. 35 days. .



11


12


His (Br. 3)


6.0 X 4.5 mm


35 X 38 mm


4.




11.0 mm.


5.3 X4.6 X 4.5 mm.. .


33 X 27 :-- 15 mm...



34.0 days.


Table VI. — Embryos Over Five Weeks Old.


His (Dr. 1) .. His (S. 3) ... His (Lhs.)...

No. CVI

No. XVH .... No. XLII .... No. CXLIV . .

No. V

No. XXV III . No. LXXXI. . No. XCIV ... No. XXII....

Minot

His

No. LVII .... His (Wt.) ... No. LXXII .. No. XXVII . . His (Lp.).... No. XXXI ...

No. VI

No. cxxvir . No. CXXVIII No. CXVIII. . His. (Dr. 2 1.. No. XCIX . , . No. XLV .... No. XXVI ...

Minot

No. LXXIX . No. OXXIX .. No. GXLV...

No. Lll

No. XGVI . . . No. XGV ....

No. CV

No. XXX. .. No. Wl\ .... No. XI.IX ...

XXIII ...

XXXIV,.

CXLVl ..

GXVII ..

GXXXVIl

CXLIX. No. XCV'III. .\'o. XLVI ..

I 'XXI ..


No. No. No. No. No. No.


No.


Length

of embryo.


15.0 15.0 17.0 17.0 18.0 18.0 18.0 18.5 19.0 30.0 20.0 20.0 33.0 33.0 33.0 23.0 33.0 23.0

».o 24.0

.'4.l) 24.0 .24.11 25.0 ,35.0 37.0 38.0 1 30.0 t 33.0 1 32.0! 33.0 1 33.0 1 33.0] 44.01 4i;.0l 48.0 I tlll.Ol 70.0 r 70.01 70.0 1 811.01 95.0 I 100.0 I 112.1)1

l.ai.ii KiO.O 135.0 210.0


nmi. mm. mm. mm.

mm. mm. min. mm. mm. mm. mm. mm. mm. mm. Mini, mm.


mm mm imn mm mm


mm mm mm


Dimensions ol umbilical vesicle.


0.0 ?< 5.5 mm . . 5.5 4.5 mm . .


Dimensions of ovum.


X 40

X 28


mm. mm.


X 30 ram. X30 X30 X 30 X 55 X40 X30


X20


X30 mm. X 20 > 35 X 30 X30


mm. una


mm irim mm. mm


mm X .50 X 30 mm. X50 X30

X 45 ■■ 40


mm. mm.


mm.. X30i


X 40. mm. .


mm . ■, 3ii 1


I X .50 )X30


X 40 X15


40

OR ,.; 50 X .50 11


mm mm.





51 days. 54 days.


47 dLiys.


■53 days. 50 days.


00 days. 77 days, 84 days, 76 days, 94 days.


Probable age.


I days


75davs, 08 days, 91 days, 05 days, 78 days.


84 days, 83 days, 83 days, 77 da\s, 90 days, 05 days.


da,\s


104 dm 115 days, 101 days, 127 davs. 1,25 days, 125 days, 143 days, 190 days.


References, or from whom obtained.


Anat. mensch. Embryonen. Anat. mensch. Embryonen. Anat. mensch. Embryonen. Dr. Gardner, Baltimore. Dr. (.'iittrell, Louisville, Kv. Dr. Wills, Los Angeles, Cal. Dr. Watson, Baltimore. Dr. Kittridge. Nashua, N. H. Dr. Sewall. Denver, fol. Dr. Brauham, Baltimore. Dr. Knill, Detroit, Mich. Dr. Snively, Waynesboro, Pa. Minot's Embryology, 392. Anat. menseh. Embryonen. Dr. Howard, Cleveland, (.ihio. Anat. mensch. Eiubrv*.'nen. Dr. Arthur, Baltimore. Dr. Thayer, Baltimore. Anat. mensch. Embryonen. Dr. Ballard, Baltimore. Dr. G o. Miller, Baltimore. lir. A. T. (.iundry, Baltimore. Dr. Lupton, Baltimore. Dr. Booker, Baltimore. Anat. mensch. Embryonen. Dr. Garr, Durham, N. C. Dr. Douglas, Nashville, Tenn. Dr. Simon, Baltimore. Human Embryology, 398. Iir. Briggs, Biackviile, S. C. Dr. (iunilry, Baltiiuore. I'r. Watson. Baltimore. Dr. (;avin, Baltimore. Dr. Spencer, ,'^an Fram-isco. Dr. Watson, Baltimore. Dr. Wats.in, Baltimore. Dr. Snively, Wavueslioro, Pa. Dr. Ballard, Baltimore.

Dr. Snively, Waynesboro, Pa. Dr. Ellis, Klktim, Md. Dr. Watson, Baltimore. Dr. Ballard, Baltimore. Dr. Watson. Baltimoie. Dr. lloen, Baltimore. Dr. Atkins(m, lialtiiiiore. Dr. Taylor. Baltiiimre. Dr. Ballard, Baltimore.



Table VII. - EXTREME and Average measurement IN MiLLIMETKEB OF THE EmBKYO AND ITS appendages

AS Obtained fuom Tables 1. to VI.


Week.


Seeond

First ball of third

Second lialt of tliird.

FourtLi

Fifth


Measurement.


Kxtreme *.

Averajre

Extreme . . Average.. . F.xtreme . . Average... Extreme . . Av<'raKe. .. Extreme . . A \eraif e. . . Extreme . . Average... Extreme . . Average.. . Extreme . . Average. . . Extreme . . Average...


Lengtti of emliryo.


0.19 to 11.7!)

2.1 to 2.41

3.2 to 4.«T

(;..■•) to

7.34 II) to 1

n.B 1.") to

17.3 2(1 to

•» r.

2.') to

26

30 to


3 li K

3.11 1<\ 24 28 •IS


Greatest lUmensions of the iiiii)5ilical vesiele.


U.l'.i to 1.8

1.14

l.o to 3

'i.r< to 4

3.3 4 to 7

4 to B

.'j.2 5.5 to « 

5.7


(ireatest

rlil))ensloiis of the

chorion.


Probable age in days.


3 t^-. 10

5.7 to 18

11.7 14 to ;30

>) 18 to 45

2li 30 to 40

32 35 txi .50

41 30 to 05

47 40 to 45

42 40 to OS

54.5


10 to 14

12 12 to 15

14 U to 23

19.5 2=5 to 28

26 32 to 37

34.0


The extreme measurements of the umbilical vesicle and chorion are the greatest measurements in each case.


ical specimens we obtained which may prove to be of the greatest practical value. The best and most convenient method of preserving young emhryi/s is to place the unopened ovum, 'with the least possible Imndluig, in. a large ijiiantity of t'cry strong alcohol. The alcohol of druggists is in no case too strong, and, according to my experiI'Dce, 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 may be a method of preserving museum specimens, but it practically )-uins every embryo which is preserved in this way. When an ovum is placed iu, say, four ounces of strong alcohol, the water of the iivum dilutes the alcohol to a iiropcr strength.

Those physicians who have the proper opportunities should place the specimen as soon as possible, and witho)it opening the ovum, in seventy pcr-ceut. alcohol, i.e., absolute alcohol reduced by volume to seventy per cent. At the end of a day or two it should be placed in fresh alcohol of the same strength. An excellent method lor meservino- embrvological specimens is to place the meni branes, blood anil allin a weak solution (live to ten per cent.) of formalin. , . .

A second convenient niethod is to place a specimen in ..uitealarge quantity of Muller's tluid, to be change, once or twice during the fiist te^y days, after which may be preserved in the same fluid indefinitely. 1 he embryo s fully hardened in about a month, an<l then i can bl washed in water for a .lay or two, alter winch it is to be preserved in seventy-per-cont. alcohol

Ten percent, nitric acid is a convenient and a most excellent method. The ovum is to be placed m four or

ixoun'L of a ten-percent solution and opened while in the fluid, care being taken not .'"I,""' /' ^ "^'^,fd According to its size (if not over an uteh ong t .should ,-cmain in the acid for from thirty mmu es t" * " J^,"";^' At the end of this time it is to be placed m seventy-pci

'X.ter"excellent method is to employ saturat«l ^nueous corrosive sublimate. The specimen is to be Z ed asTn the ten-per-cent. HNO. only it >«'. remain in The sublimate longer. These specimens are then to be preserved in seventy-pcr-cent. alcohol.

There are many other methods, but it an) oi luc above are cmployc^d there will be a sufficient supply o mateHal to aid the study of l^"™an em brydogy. I really wonderful to see what progress has .'f this study when we consider how diftcult it is to ohtdin preserved human embryos, as a glance at the man| pers of His and at the excellent text-book of Minot.ll

Ti^reat work is done when the specimens are once obtained, but in order to make it complete they must placed in the hands of a specialist, who can devote all his energies as well as all the additional necessary expense to these the most precious of embryological specimens.


Franklin P. Mall.


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