282 



EVOLUTION AND ANIMAL LIFE 



and an effect, presumes 

 to say that all these 

 phenomena may be 

 much more nearly of 

 the same sort than we 

 are accustomed to con- 

 sider them to be. The 

 biological mechanists 

 believe, in a word, that 

 all vital phenomena 

 will in last analysis 

 prove to be truly phys- 

 icochemical phenom- 

 ena; that organisms 

 show in their reactions 

 no new forces or prin- 

 ciples, but that their 

 behavior is only an im- 

 mensely complex interplay of the same forces and activities 

 already known to us in the inorganic world. 



And their belief is not wholly without some basis of observed 

 or experimentally proved fact. Many of the simpler so-called 

 vital phenomena, especially the movements of the simplest 



Fig. 164. — Regeneration in Hydra viridis: A, Nor- 

 mal hydra (lines show where piece was cut out) ; 



B, 1-4, changes in a piece of A as seen from side ; 



C, 1-4, same as seen from end ; D, E, F, later 

 changes in same piece. (After Morgan.) 



Fig. 165. — Regeneration of Stentor cwruleus: A, Cut in three pieces; B, row showing 

 regeneration of the anterior piece ; C, regeneration of middle piece ; D, that of 

 posterior piece. (After Morgan.) 



