202 TRANSMISSION 01 ACQUIRED CHARACTERS 



a change tending to bring the actions of all organs, reproductive 

 included, into harmony with these new actions," or inactions. 

 The modified aggregate impressed some corresponding modifica- 

 tion on the structures and polarities of the germ-units. And 

 this was how Herbert Spencer had small hands. At least, so 

 he tells us. 



Disuse of Parts. — It seems " natural " to suppose that 

 organs have dwindled pari passu with their disuse, and because of 

 their disuse. But the two statements are not synonymous. The 

 dwindling may be due to germinal variations in the line of reduc- 

 tion, which are appropriate because of some change in the ani- 

 mal's habits and environment. It may even be that the organism 

 meets an endogenous reduction of certain parts by itself changing 

 its habits and habitat. Moreover, it is important to notice, as 

 Emery, Kennel, and Ziegler have pointed out, that there has pro- 

 bably been a " Kampf der Theile im Organismus " (a struggle 

 of parts within the organism) not merely in individual ontogeny, 

 but also in the racial phylogeny. Dwindling of one part occurs 

 when some adjacent part attains increased differentiation. 

 " Thus snakes have not lost their limbs because they did not use 

 them, but because of their evolution in the direction of excep- 

 tionally large trunk and tail musculature. In man the strong 

 dentition of his Simian forebears has become weaker, not through 

 disuse, but because the extraordinary increase of the brain has 

 been correlated with a weaker development of other parts of the 

 head " (H. E. Ziegler, 1905, p. 3). 



§ 8. General Argument for tJie Transmissibility of Modifications 



The Germ- cells are not Insulated. — While it must be ad- 

 mitted that the germ-cells have a certain apartness from the daily 

 life of the body, and that they are unspecialised cells that have 

 not shared in the differentiation characteristic of the body-cells, 

 is there not some risk of exaggerating the distinction between 

 somato-plasm and germ-plasm ? 



