Jill: I U.IAI. VI .MM: \Sl.s "I MAN. 1M 1 



CHAPTER XIII. 

 Tin: r<i'i\L I//:.)//;// i VS8 OF .'/ 1 v. 



Tin: investigation of tin- first .xiage-; in the development of man, 



which are accomplished during ihfiir.xt tour week- of pregnancy, is 



(( ujl< (1 with extraordinary ditliculties. Only very exceptionally does 

 the embryologiM comeinto p i of young liuiuan ova. whether 



found in the uterus at the time of di.-.-eet ion, or coming into the 

 hands of a physician as (he re.-ult of miscarriage. In tin- l.-i 

 the ova have often been dead fur a long time in the uterus, and 

 consequently are in process of decomposition. Finally, a good 

 preservation and an accurate in\e.-tigation of Mich small and 

 delicate objects demand no slight decree of .-kill. 



This accounts for the fact that \\e do not possess in the case of 

 Man a single observation upon the process of fertilisation or that of 

 cleavage, upon the formation of the germ-layers, or upon the lir>t 

 establishment of the form of the body, the fu-tal m mln-anes. and a 

 large number of other organs. ( 'oncerning this whole period we 

 are dependent upon the conclusions which are furnished by the 

 development of other Mammals. Thus we assume t hat fertilisation 

 normally takes place in the enlarged beginning of the oviduc! 

 (Fallopian tube) j that the seminal element.-, which remain alive in 

 the female sexual organs perhaps for days or weeks, here await the 

 ovum as it emerges from the ovary ; that the ovum already segmented 

 enters into the cavity of the uterus, attaches itself in the mucous 

 membrane, and during the first weeks of piegnancy gives rise to the 

 g rni-layers. the outer form of the b< dy, and the fostal membrano, 

 according to the well-known rules for other Mammals. 



A little, although very scanty, information has been acquired, 

 but this concerns only the second and subM-quent week. A >mall 

 number of ova have been described in the literature, which for the 

 most part come from miscarriagi -. and the age of which has been 

 -tiinated at from twelve to fifteen day-. The bla.-todermic \e-icles 

 measured . r > to U mm. in diameter. Here belong two ova de>cribed 

 by ALLKX THOMSON, and those i >M:I; \. j. KOI.K. HI:N\I... 



Ki h iiKKT, UIIKI -s. r.i:K,i;i. IND Lowi:. as well as the cases published 



by AHI.FKI.I). KOI.I.M\NN, POL, and G] 



Upon critical comparison of the di>co\vrie>. there are two facts 

 which we can regaid as e>talli>l.ed. 



At the end of the second week the blastodermic vesicle 



16 



