54: THE PLAY OF AXIMALS. 



belonging to the one individual; but the other passes 

 over to succeeding generations and determines the colour 

 of their wings so far as they are not further modified 

 by later temperature conditions." It is only by means 

 of such variations in the germ structure, brought about 

 by external influences, that Weismann can now find a 

 possible explanation of the origin of new species.* 



I now pause to gather up these positions. Weis- 

 mann's theory is not sufficiently defined by the thesis: 

 there is no inheritance of acquired characters; for, in 

 the first place, he grants such inheritance in the case 

 of unicellular structures without a nucleus, where his 

 distinctions between morpJio plasm and ideoplasm, soma- 

 togen and hiastogen do not hold; and, secondly, while 

 there is indeed for him no inheritance of acquired 

 characters among individuals of the higher forms of 

 life, there is the inheritance of the acquired charac- 

 ters of germ plasm. For conditions which infiuence an 

 individual organism may take effect in the hereditary 

 substance present in it and produce inheritable changes 

 in that substance. Acquired variation in the individual 

 may run parallel, under certain conditions, with acquired 

 and inherited variation in the germ plasm, but is never 

 the cause of it. They are simultaneous reactions from a 

 third condition — namely, the external influence. So it 

 appears that what is usually meant by the phrase in- 

 heritance of acquired characters — namely, the carrying 

 over from one generation to another of acquired charac- 

 ters of the body — is actually excluded by Weismann's 

 theory, f 



* Keim plasma, especially pp. 542. 544, 54G. Sec also G. J. Ro- 

 manes's Examination of Weismannism. 



f I can not resist citins: Kant here as an advocate of the old 

 preformation doctrine. In 1775 he said in his article on The 



U-^ 



