500 A. W. BELLAMY 
for their appearance are less often realized, abnormalities showing 
differential acclimation or recovery, or differential acceleration. 
Often the embryo shows a combination of inhibition and aceli- 
mation or recovery or both. The failure to distinguish these 
different types when seen in the same embryo may lead to some 
confusion in attempting to interpret abnormal development. I 
do not, of course, intend to imply that all abnormalities are 
consequences of conditions which, operating relatively early in 
development, produce differential inhibitions, accelerations, 
acclimations, or recoveries. Mechanical disturbances and the 
like and probably other disturbances coming near the end of de- 
velopment belong to quite a different category. With the great 
majority of teratological forms falling readily into the classes 
mentioned above or combinations of them which in turn must be 
consequences of differential susceptibility, the task of interpret- 
ing teratological development resolves itself largely into a matter 
of accounting satisfactorily for differential susceptibility. 
The reasons for regarding differential susceptibility as one 
expression of underlying graded differences in the dynamic re- 
lations and activities of protoplasm—physiological gradients— 
have been presented elsewhere (Child, ’20; Bellamy, 719). 
Given the organismic pattern as a gradient or gradients in 
fundamental functional and structural relationships in a specific 
protoplasm, and there is abundant experimental evidence to sup- 
port this idea, teratological development becomes understandable 
as a disturbance of this underlying order. Since this order is a 
graded one paralleling the axes of symmetry of the organism, any 
considerable disturbance of it must also entail a parallel and 
differential modification in the development of the embryo. 
SUMMARY 
1. The egg and embryo of the frog exhibit a differential sus- 
ceptibility to a great variety of conditions that disturb develop- 
mental processes. 
2. According to the experimental treatment and the physio- 
logical condition of the organism at the time of exposure, the 
induced modifications fall naturally into classes of differential 
