390 



BERTRAM G. SMITH 

 DISCUSSION 



A. Bilateral organization previous to fertilization. In the egg 

 of Cryptobranchus allegheniensis we find polarity arising dur- 

 ing ovogenesis and bilaterality established only after cleavage 

 has reached an advanced stage. The writer's observations 

 give no support to the idea sometimes advanced that "bi- 



Fig, 32 Sagittal section of a beginning gastrula of Cryptobranchus allegheni- 

 ensis. B, blastopore; S, segmentation cavity or blastocoele; Y, yolk. The 

 drawing was made with the aid of a camera lucida. X 15. 



laterality as well as polarity are inherent characters of the 

 protoplasm and persist from generation to generation" (Bartel- 

 mez, '12). In many species of animals the egg is bilaterally 

 organized before fertihzation, but it has never been shown that 

 this bilateral organization is present as such from the beginning 

 of ovogenesis. The available evidence favors the theory of nu- 

 clear determination, as opposed to the hypothesis of cj^toplasmic 

 inheritance. 



