124 THE THEORIES OF EVOLUTION 



The former, clustered more closely, make up a more 

 solid and less aqueous mass; the others constitute a 

 more fluid protoplasm containing more water. The 

 micella? which have a definite orientation make up 

 the idioplasm or germ plasm, the others make up the 

 nutritive plasm. 



The difference between the two plasms is consid- 

 ered by Naegeli as supremely important; it has also 

 become a fundamental principle of Weismann's 

 theory. It is the idioplasm which, under different 

 names, is, according to both theories, the origin 

 of all vital phenomena, upon which depend all the 

 characters of living things, and which is the basis of 

 heredity. 



According to Naegeli, the idioplasm appears in the 

 primitive plasm in the shape of scattered particles. 

 These particles multiply and unite so as to form fila- 

 ments, then cords which gradually constitute a con- 

 tinuous network. That network spreads all through 

 the organism of the animal or plant, from one cell to 

 another, passing through the microscopic pores of the 

 cell's envelope and invading the nucleus as well as the 

 cytoplasm. The idioplasm reacting upon the various 

 tissues and substances of the organism imparts to 

 them their various characters, shape or colour. Here 

 we encounter a first difficulty. As nothing indicates 

 that the micella? themselves have different characters, 

 whence come the various characters they impart? In 



