42 DEGENERATION : I 



besides legs and muscles, lost by the diminutive de- 

 generate descendants of a larger race. That this is a 

 possible course of change all will, I think, admit. It 

 is actually exemplified in Appendicularia — the only 

 adult representative of the Ascidian tadpole — still 

 tadpole-like in form and structure, but curiously de- 

 generate and simplified in its internal organs. This 

 kind of degeneration is also exemplified in the Eotifers, 

 or wheel animalcules, in the minute Crustacean water- 

 fleas (Ostracoda), and in the Moss-polyps, or Polyzoa. 

 Roughly then we may sum up the immediate ante- 

 cedents of degenerative evolution as, 1, Parasitism ; 2, 

 Fixity or immobility ; 3, Vegetative nutrition ; 4, Ex- 

 cessive reduction of size. This is not a logical enu- 

 meration, for each of these causes involves, or may be 

 inseparably connected with, one or more of the others. 

 It will serve for the present as well as a more exhaus- 

 tive analysis. (See Note C.) 



And now we have to note an important fact with 

 resfard to the evidence which we can obtain of the 

 occurrence of this process of degeneration. We have 

 seen that the most conclusive evidence is that of the 

 recapitulative development of the individual. The 

 Ascidian Phallusia shows itself to be a degenerate 

 Vertebrate by beginning life as a tadpole. But such 

 recapitulative development is by no means the rule. 

 Quite arbitrarily, we find, it is exhibited in one animal 

 and not in a nearly allied kind. Thus very many 

 animals belonging to the Ascidian group have no tad- 

 pole young — ^just as some tree-frogs have no tadpoles. 

 It is quite possible, and often, more often than not. 



