6 



N. YATSU : OBSERVATIONS AND EXPERIMENTS 



1. Removal experiments performed prior to 

 the formation of the polocytes. 



A portion of cytoplasm was cut off before the polocytes were 

 formed ; most eggs were operated before fertilization : some may have 

 been cut after it. It was extremely difficult to determine the exact 

 moment of fertilization. Moreover at this time there is no landmark 

 to orient section planes ; the record was necessarily incomplete. 



Of thirteen cases eleven had eight rows of comb-plates, while 

 two had seven rows (Fig. i). In two cases the number of comb-plates 

 was smaller than in the normal embryos. In one case one of the 

 entodermal pockets was short ; in another two of them were short 

 (Fig. 2). Excepting these defective cases all the rest were normal. 

 Judging from the size of resulting embryos a considerable amount of 

 cytoplasm must have been cut off in some cases, yet those produced 

 from such pieces were quite normal. This taken with the fact that 

 sectioning were performed at random, it may not be amiss to infer 

 that the germinal stuffs for the future comb-plates and for the entodermal 

 pockets have not yet been well localized. 



For the sake of comparison some eggs were cut in two between 

 the formation of the polocytes and the beginning of the first eleavage. 

 Of ten eggs thus operated upon three were perfect, all the others 

 being more or less defective, as FlSCHEL has found out ('03). 



The above two series of experiments will show that there is a 

 decided advance in the specification of germ-regions after the formation 

 of the polocytes. 



Driesch and MORGAN ('95 pp. 217-219) describe sixteen 

 embryos resulting frow the removal of a certain amount of cytoplasm 

 from the egg from three to four hours prior to the first cleavage. 

 But since the exact time of operation in relation to both fertilization 

 and polocyte formation has not been recorded, their results cannot 

 directly be utilized for the question under consideration. 



