320 STUDIES IN GENERAL PHYSIOLOGY 
development of an embryo would, according to this, be in a 
physiologico-chemical sense an epigenesis and no evolution. 
In order to test this idea, I made experiments on the rela- 
tive sensitiveness of the embryo in the various stages of its 
development. I thought that sudden changes in the sensi- 
tiveness during the transition from one developmental stage 
to another would speak for epigenesis. Such a change in 
reaction was, indeed, found in the experiments on loss of 
water. 
I have begun experiments similar to those on Fundulus 
on Perca fluviatilis. The physiological reactions of the 
embryo of Perca are, however, very different from those of 
Fundulus, as was to be expected from the beginning 
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