WEISMANN'S THEORY 137 



ual which is to grow out of an id is determined in its 

 life as well as in its nature by a corresponding particle 

 of germ plasm. Those particles are therefore desig- 

 nated as "determinants" (Vererbungstilche) . 



Here we encounter a difficulty. We might assume 

 that there should be in the germ plasm as many de- 

 terminants as there are cells to be determined in the 

 adult individual at every stage of its development. 

 This is not necessary ; there must be as many of these 

 as there are regions in the fully-formed organism 

 capable of independent and transmissible variation, 

 including all the stages of development. 1 



It is a well-known fact that the most dissimilar 

 characters may vary independently. Every part of 

 a butterfly's wing may vary independently from the 

 adjoining parts, as is shown by variations in colour- 

 ing; every part must therefore be represented in the 

 germ plasm by an independent element, by a special 

 determinant; at the same time, the id of a butterfly 

 must also contain the determinants of all the variable 

 regions of the caterpillar. As on the other hand all 

 the red particles of the blood and all the hepatic cells 

 of the liver "in all probability only vary en bloc" one 

 single determinant suffices to represent them all. 



The determinants have a concrete existence, for 

 there must be in the plasm something which causes a 

 certain structure or character to be present or lacking. 



i The Evolution Theory, p. 360. 



