2 o2 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



reflexes ? Either the apparent simplicity of the struct- 

 ure of the egg is only an illusion, and in reality the 

 structure of the egg is no less complicated than the 

 full-grown animal, or the sum of the elements which 

 we call the form and instincts of the full-errown ani- 



o 



mal is only the resultant of a few simpler elements 

 which can readily be transmitted through the egg 

 without its possessing a complicated structure. The 

 discussion of the mechanics of instincts in the last 

 chapter shows the latter to be the case. Let us con- 

 sider those instincts that depend on heliotropic reac- 

 tions for instance, the flying of the moth into the 

 flame. This instinct is unequivocally determined, first, 

 by the presence of a substance in the surface of the 

 animal which is sensitive to light, and second, by the 

 symmetrical structure of the animal. For the trans- 

 mission of a substance which is sensitive to light 

 through the egg no complicated mysterious structure 

 is necessary. Neither is a complicated structure 

 necessary for the egg in order that it may transmit 

 the symmetrical relations of the animal. 



For the inheritance of form the conditions are not 

 very different. The egg is not the bearer of the form 

 of the full-grown animal, but of certain chemical sub- 

 stances, especially of ferments. According to the 

 stereochemical configuration of the latter, the products 

 of assimilation, and with these the materials of the 

 body, turn out differently. The process of develop- 

 ment is not only a morphological but a chemical dif- 

 ferentiation, and new combinations of substances are 



