RE GENERA TION. 1 9 3 



in correspondence with the increase in complexity of organiza- 

 tion ; but that it may, on the other hand, be increased by special 

 selective processes in each stage of its degeneration in the case 

 of certain parts which are physiologically important and at the 

 same time frequently exposed to loss." 



There are many points in these quotations that are, I think, 

 open to criticism, but it would lead me too far were I to attempt 

 to discuss them. Yet I cannot let this opportunity go by with- 

 out calling attention to another point raised by Weismann in 

 his later article. He says : " It may not have occurred to 

 Morgan that the changes in the structure of a species may 

 have kept pace with the changes in the conditions of its life ; 

 yet this is a presupposition of the hypotheses of natural selec- 

 tion, and is, indeed, its conditio sine q?ia noji. Hermit crabs 

 have certainly possessed the power of regeneration ' from the 

 beginning'; but may they not have inherited it from their ances- 

 tors, the long-tailed forms, which possess it to this day, and have 

 need of it for all their appendages, since all are liable to injury } 

 And cannot, nay must not, these in their turn have inherited it 

 from their ancestors, the sessile-eyed crustaceans, and so on, 

 through the whole crustacean pedigree, back to the unknown 

 annelid-like ancestors of the class .-'... It seems almost as if 

 Morgan ascribed to me the view that the capacity for regenera- 

 tion must be built up anew for each species — must be inscribed, 

 so to speak, on a tabnla rasa ; my view, however, is that here, 

 as in all transformations, nature started with what was already 

 present, and by modifying it brought about adaptation to new 

 conditions. The assumed general power of regeneration in the 

 lowly ancestors of the crustaceans would thus gradually have 

 adapted itself to the changes in the body and to the new con- 

 ditions resulting from these changes as well as from other 

 causes ; it would have become localized and specialized. . . . 

 As in the course of time the appendages of the different 

 body-segments became more widely differentiated in adaptation 

 to different functions — giving rise to antennae, jaws, walking- 

 legs, or swimmerets — the predisposition to regenerate in certain 

 parts of the body slowly varied also ; and thus, not indeed at 

 the same rate, but not lagging very far behind, the adaptation 



