50 7'HE ORGANIC GROWTH OF THE LIVIXG WORLD sec. 



whether new forms coiikl not be generated b}^ internal 

 germs or external buds. In support of this the phenomena 

 of alternation of generations are adduced. 



Thirdly, it would have to be- considered whether not onl}^ 

 germs and buds, but free-living young forms of animals are not 

 capable of entering upon a development other than the typical. 



Lastly, the possibility of a " rapid modification of adult 

 organisms into others " is considered. 



In all these cases we should have a sudden evolution, " yet 

 this is essentially to be traced to the embryonic period, and, 

 indeed, to its first stages." 



In addition, a more gradual modification in a less degree is 

 recognised as possible, and some effect is ascribed to it, and 

 this likewise is chiefly to fall within the embryonic period. 



We should have, therefore, I said in my " Variation of the 

 "Wall-Lizard," "an upward evolution towards higher forms, 

 from internal causes. Original organisms — ova — must, ac- 

 cording to this, have developed all at once into higher 

 forms, e.g. into mammals, and they would have succeeded in 

 this just the same wherever they happened to be, no matter 

 what the external conditions in which they lived or were 

 about to live. Adaptation has nothing to do with the 

 question — whether a part newly arising is useful or harmful is 

 of no consequence ; it is as if the whole course which the 

 original organism had to pass through was definitely pre- 

 ordained for it by internal causes, and as if this plan (the 

 w^ords plan of evolution are repeatedly used, and used as if 

 equivalent to * general law of nature ') corresponded from the 

 beqinnin^f to the external conditions." 



Kolliker also explained, although not in his first paper on 

 this subject, yet later, that his internal causes were physico- 

 chemical. 



The facts on which my conception of the modification of 

 species is based show, in harmony with those brought to 



