478 WM. E. KELLICOTT 



sex products upon each other showing only at later cleavage 

 and subsequently;" that gastrulation, i.e., the formation of the 

 germ layers — the most marked of the earlier differentiations of 

 the embryo, was a period of high mortality; that numerous ab- 

 normalities appeared in the hybrid embryos surviving this 

 period. He interpreted this to signify that the sex cells exer- 

 cised a poisonous action upon each other, preventing normal 

 development, and suggested as an analogy, merely, the toxic 

 effects of transfused bloods. Loeb also noted that various 

 abnormalities were not infrequent among heterogeneous hy- 

 brids, especially in respect to the circulatory system and eyes, 

 and suggested that the small size of the embryos thus produced 

 might be due to their failure to digest the yolk as rapidly as 

 the pure bred embryos. 



Newman similarly finds the period of gastrulation one of high 

 mortality, but he shows that the effect of the 'foreign' sperm 

 may frequently be detected even during the earlier cleavage 

 period. He also refers to the variety of abnormalities that may 

 appear during the later development of those embryos surviv- 

 ing the gastiulation period, and partially relies upon the nutri- 

 tion hypothesis to explain them. However, since the problem 

 he was investigating was an entirely different one, he does not 

 attempt a careful analysis of the probable causes of abnormal 

 development, and it would be unfair seriously to criticise his 

 suggestion that death or abnormality during gastrulation is due to 

 failure to establish nutritive relations with the yolk, which is 

 to be regarded rather as a passing suggestion than as a definite 

 opinion. I do not understand that he, or anyone, has demon- 

 strated that this period is especially characterized by the estab- 

 lishment of such relations with the yolk. 



It is of considerable importance from my point of \aew to 

 note that Newman finds that one of the common effects of 

 hybridization is a disturbance in the time relations of various 

 processes of development, both acceleration and retardation 

 being quite common consequences. This means that not only is 

 there a disturbance of the normal morphological sequences in 

 ?uch hybrid organisms, but th? t the whole organizational, in- 



