30 J. P. HILL. 



shaped piece lias been gouged out at tlie upper pole. 

 Consequently, when it divides along its polai- diameter, the 

 resulting blastomei'es will have the form of hemispheres with 

 obliquely truncated upper surfaces or ends, which will be pro- 

 portionately thicker than the lower ends. In correlation 

 therewith we find the nucleus of each blastomere situated 

 slio'htly excentrically, rather nearer the upper than the lower 

 pole (fig. 18). The rounded yolk-body lies partly enclosed 

 betAveen the upper truncated surfaces of the blastomeres. 



Two-celled eggs are shown in vertical section in figs. 17 

 and 18. The cytoplasm of the blastomeres exhibits a well- 

 marked differentiation into two zones corresponding to that 

 already seen in the formative cytoplasm of the unsegmented 

 egg, only much more accentuated, viz. a dense, fine-grained 

 perinuclear zone, and a less dense, more vacuolated peripheral 

 zone, in which there is present a coarse, irregular network of 

 deeply staining strands, recalling the framework of mito- 

 chondrial origin described by Van der Stricht ('04, '05) in 

 the hiniian ovum and that of Vesperugo. We have here in 

 this differentiation of the cytoplasm, evidence of the occur- 

 rence of an intense metabolic activity which has resulted in a 

 marked increase in the amount of deutoplasmic material 

 present in the blastomeres as compared with that found in 

 the ovarian egg or even in the unsegmented uterine egg. 

 The blastomeres consequently present a somewhat dense 

 opaque appearance when examined in the fresh state, their 

 nuclei being partially obscured from view. Amongst the 

 Eutheria, various observers (Sobotta, Van der Stricht, Lams 

 and Doorme) have described a similar increase in the deuto- 

 plasmic contents of the egg after its passage into the 

 Fallopian tube or uterus. 



The second cleavage plane is also vertical and at right 

 angles to the first. The resulting four equal-sized blastomeres 

 viewed from the side (PI. 2, fig. 19) are seen to be ovalish in 

 outline, their lower ends being slightly narrower and more 

 pointed than their upper ends, which diverge somewhat to 

 enclose the lower part of the yolk-body. Seen from one of 



