66 THE SURVIVAL OF THE UNLIKE. [ll. 



When organisms became complex, it was necessary 

 to assume either that the soma -plasm does or does not 

 directly influence the germ -plasm. Weismann discarded 

 the various hypotheses which suppose that there is a 

 vital and necessary connection between the body units 

 and reproductive units, and then to avoid the difficulties 

 which the hereditability of acquired characters would 

 entail, he supposed that such characters are not heredi- 

 itary. His subsequent labors have been largely em- 

 ployed in trying to show that they are not. This sup- 

 position was made for the purpose of simplifying the 

 hypothesis by removing the cumbrous gemmules of 

 Darwin and the similar bodies or movements of other 

 philosophers, and, therefore, by localizing the seat of 

 the germ -plasm. But he immediately encounters diffi- 

 culties quite as great as those which he avoids. In 

 cases where there are alternate generations of asexual 

 and sexual organisms, he must suppose that the germ- 

 plasm is united with the soma -plasm, and is probably, 

 therefore, distributed throughout the body. "There 

 may be, in fact, cases," Weismann writes, "in which 

 such separation [of the germ -plasm from the soma- 

 plasm] does not take place until after the animal is 

 completely formed, and others, as I believe that I have 

 shown, in which it first arises one or two generations 

 later, viz., in the buds produced by the parent." And 

 he has been compelled to admit that in the case of be- 

 gonias, which are propagated by leaves, the germ -plasm 

 is probably distributed throughout the foliage; and he 

 must make a similar admission for all plants, for they 

 can all be ])ropagated and modified through asexual or 

 vegetative parts.* (Compare Essay III.) This is ad- 



* Throughout these essays, I have used the terms " asexual " and " sexless " 



