52 DEGENERATION, 



That this is a possible course of change all will, I 

 think, admit. It is actually exemplified in Appen- 

 dicularia — the only adult representative of the 

 Ascidian tadpole — still tadpole-like in form and 

 structure, but curiously degenerate and simplified in 

 its internal organs. This kind of degeneration is 

 also exemplified in the Rotifers, 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 antecedents of degene- 

 rative evolution as, i, Parasitism ; 2, Fixity or 

 immobility ; 3, Vegetative nutrition ; 4, Excessive 

 reduction of size. This is not a logical enumeration, 

 for each of these causes involves, or may be insepa- 

 rably connected with, one or more of the others. It 

 will serve for the present as well as a more exhaustive 

 analysis. (See Note C.) 



And now we have to note an important fact 

 with regard 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 



