142 THE PHILOSOPHY OF BIOLOGY 



a monstrous larva ought to result, for the first nuclei 

 separated from each other have been forced into 

 positions altogether different from those which they 

 should have occupied had they developed normally. 

 Yet on releasing the pressure readjustment takes 

 place. New divisions occur so as to restore the normal 

 form of larva. The Roux-Weismann subsidiary 

 hypothesis is that the stimulus of the pressure has 

 compelled the nuclei to divide at first in such a way 

 as to compensate for the disturbance. 



Let us remove some of the blastomeres. On the 

 original hypothesis the determinants for the structures 

 which the nuclei of these blastomeres contained have 

 been lost . These structures should , therefore , be missing 

 in the embryo. But nothing of the sort is the result. 

 Other nuclei divide and replace the lost ones, and the 

 embryo develops as in the normal mode. The reply 

 is that in addition to the determinants which were 

 necessary for their own peculiar function, these nuclei 

 contained a reserve of all others. On disturbance 

 these determinants, " latent " in all other conditions, 

 became active and restituted the lost parts. 



Let us remove some organ from an adult organism. 

 The most remarkable experiment of this kind is the 

 removal of the crystalline lens from the eye of the 

 salamander. Now the lens of the eye develops from 

 the primitive integument (ectoderm) of the head, but 

 the iris of the eye develops mainly from a part of the 

 primitive brain. After the operation a new lens is 

 formed from the iris and not from the cornea. There- 

 fore the highly specialised iris contains also deter- 

 minants of other kinds. Does it contain those for 

 itself and lens only, or others ? If it contains many 

 kinds, then we conclude that even the definite adult 

 structures contain determinants of many other kinds 



