THEORY OF THE DEVELOPMENT OF ORGANISMS 13 



distinct from each other as in the adult condition. 

 The species is present as truly in the fowl's egg as 

 in the fowl, and the egg of a fowl differs as much 

 from the egg of a frog as the fowl differs from the 

 frog. Men, rodents, ruminants, invertebrates display 

 more or less important and outwardly visible dif- 

 ferences in constitution ; so also the sexual cells to 

 which they give rise, since they represent the 

 rudiments of the future adults, must be different 

 from each other in the constitution of the rudi- 

 ments, although we are not yet able to prove these 

 differences by observation.' 



In this assumption of a specific and highly- 

 organized germinal substance with which a develop- 

 ment begins, I agree with evolutionists ; but in its 

 details my conception is quite different from their 

 conception. For I can ascribe to the germinal 

 substance only such characters as are appropriate 

 to the true nature of a cell, but I cannot ascribe to 

 it the numerous characters that can come into 

 existence only by the interrelations of many cells 

 and the action of the environment. 



Haacke, in his recently-published book (Gestal- 

 tung und Vererbung), has expressed a doubt that 

 my conception of development is, after all, a pre- 

 formational theory. 'For preformation,' he says, 

 ' it is not necessary to imagine that the egg contains 

 a miniature of the adult. If only, like Hertwig, 

 one assumes to be present in the germinal material 

 a prearrangement of qualitatively different idio- 

 blasts, one has steered into the harbour of pre- 

 formation with all sails set.' 



