6 



ART. 10. — N. YATSU 



Fig. II. {Cerehratulus lacteus) 



8, early cleavage stages of the egg from which the vegital region was 

 cut off at the beginning of the first cleavage ; 9, S-cell stage of a 

 normal egg, showing the size-relation between the upper and the lower 

 cells; 10a, egg cut horizontally at the 2-cell stage; 10b, same at the 8-cell 

 stage; 11a, another egg cut obliquely; lib, same at the 8-cell stage. 

 Notice that in both Figs. 10b and lib the upper cells are somewhat larger 

 than the lower. 



section, the proportion of the upper and the lower cells was normal 

 or approximately so, that is, the upper blastomeres were a little 

 larger than the lower. Fig. 10a represents an egg cut almost 

 horizontally. It one compares the 8-cell stage of this egg (Fig. 

 10b) with that of an unoperated egg, he will at once recognize that 

 the normal proportion is retained. The same phenomenon will 

 be seen in the case of an egg obliquely sectioned (Fig. 11a and b). 

 It is quite probable, though as yet not experimentally 

 demonstrated, that if the operation be performed immediately 

 prior to the third cleavage, the proportion between the upper 

 and the lower cells would be disturbed, inferring from the results 

 of Experiment A. 



