I 



356 A. W. BELLAMY. 



Even admitting that different agents do attack the proto- 

 plasmic reaction system at different points as they undoubtedly 

 do the important point is that in such a complex and inter- 

 correlated physico-chemical reaction system as protoplasm, it 

 is hardly possible to alter any one set of reactions or conditions 

 to any considerable degree, without disturbing the system as a 

 whole. Consequently in subjecting the frog egg or any other 

 developing organism to an agent that in any way inhibits proto- 

 plasmic activity to a sufficient degree, it is certainly, in its broader 

 aspects, not a specific, but a general or quantitative effect and 

 reaction of the organism to the agent that becomes apparent. 

 It is the striking uniformity of the susceptibility relations of 

 organisms to so many different agents and conditions that forces 

 the conclusion that there must be some fundamental feature of 

 all axiate organisms that is affected in much the same way by 

 different agents. In other words, it is the existence of a gradient 

 or gradients in metabolic rate, and protoplasmic conditions associated 

 with them along physiological axes in the organism, that determine 

 the uniformity and the susceptibility relations that have been shown 

 to exist, and afford the basis for a rational interpretation of terato- 



logical development. 



VI. SUMMARY. 



1. In the ovarian egg of the frog there is a definite relation 

 between the polar axis of the egg and its blood supply. In every 

 case the pigmented hemisphere is more richly supplied with 

 arterial blood than the unpigmented hemisphere. It is suggested 

 that polarity arises in response to this external factor, viz., 

 respiratory and nutritive relation of the egg to the parent body. 

 It also seems probable that the localization of the pigment on 

 the egg is in response to the greater oxygen supply over a re- 

 stricted area. There is no orientation of the ovarian egg to 

 gravity. 



It is pointed out that polarity in a number of other organisms 

 arises in response to conditions external to the egg. 



2. It is shown that differences in susceptibility exist in different 

 parts of the egg and embryo of the frog. These differences are 

 evidenced in the following ways: 



(a) By differential death gradients, 



