134 N - YATSU. 



in the Cerebratulus egg we have so far no direct evidence to sup- 

 port the occurrence of the last phenomenon, yet my observations 

 on sections clearly show that a segregation of egg material does 

 actually takes place at this period, the yolk accumulating in the 

 lower hemisphere, while the clear and more finely granular 

 protoplasm collects especially at the top of the egg, where, 

 in the iron hematoxylin-Congo-red preparations, it stands out 

 beautifully stained blue in contrast with the red yolk. After the 

 fading of the germinal vesicle the eggs not only become fecun- 

 dable, but also acquire much more power of forming cytasters 

 than they had before. It is hardly necessary to state that in 

 many forms remarkable changes take place in the egg at or 

 after the entrance of the spermatozoon. It may further be 

 pointed out, however, that the part played by the spermatozoon 

 in causing rearrangements of the egg-substance is of a subsidiary 

 character, as is shown in the case of parthenogenesis. 



To the question as to what degree of localization exists in the 

 cytoplasm of the Cerebratulus egg before the fading of the germi- 

 nal vesicle, I am not in a position to answer, and it is almost 

 impossible to find direct evidence. But the results of my experi- 

 ments harmonize with Boveri's view that there is at first only a 

 simple promorphological condition such as polarity and bilater- 

 ality, which may give a basis, so to speak, for a more definite 

 grouping of material arising at the time of the flowing-out of the 

 nuclear fluids. Otherwise it is impossible to understand the 

 sudden increase in the proportion of abnormal embryos arising 

 from the fragments obtained subsequent to the fading of the 

 germinal vesicle. In the eggs of some forms (c. g. Myzostoma) 

 the segregation of material has in a measure taken place long 

 before maturation. In such cases the horizontal section of the 

 egg before the disappearance of the germinal vesicle will, I think, 

 produce a defective embryo. My observations on the later 

 periods render it probable that at this time there must be a certain 

 number of predetermined regions more or less firmly fixed, 

 though this is not so clearly shown as in the ctenophore egg. It 

 is extremely desirable to carry out careful studies with respect 

 to the egg specification prior to the first cleavage in other forms. 



So far as I could ascertain (up to the eight-cell stage), the cleav- 



