48 THEORY OF ORGANIC EVOLUTION. 



i. The essential part of the reproductive plasm, 

 termed idioplasm, since it divides and passes over 

 from generation to generation, in higher as well as 

 in lower organisms, has a continuous or "immortal" 

 existence. * 



a. During this continuous life the idioplasm 

 goes through a development of its own, just as an 

 individual organism goes through a certain cycle of 

 development during its individual life. This devel- 

 opment consists in a constantly increasing complex- 

 ity of structure and differentiation of function. 



3. This development is aiitomatic, resulting from 

 internal forces or movements, (Vervollkommnungs- 

 bewegungen*). 



4. As a result of the increasing complexity of 

 structure in the idioplasm the entire organism, which 

 in each generation rearises therefrom, becomes, 

 from generation to generation, more and more com- 

 plex with greater and greater differentiation of 

 function. Thus the progression of the idioplasm 

 controls the phylogeny of the race. It marks out 

 the course of evolution. 



5. Since, according to Nageli, new life with new 

 idioplasms, may arise wherever and whenever the 

 necessary conditions combine, the present organic 

 world is not made up from branchings of a single 

 original idioplasm, but each race or group may 

 have its own specific idioplasm ; and, since this has 

 its own characteristic structure and its own specific 

 internal perfecting forces, it passes through its own 



Nageli's idioplasm corresponds in many respects, though by no 

 means in all, to Weismann's germ-plasm. Weismann's idea of continuity 

 or "immortality," which has been so widely noticed, Is set forth with equal 

 clearness, though with less emphasis, by Nageli. 



