FACTORS IN' ONTOGENY 



283 



and even the inore complex animals, have been shcvv'n to 

 be suggestively like motion reactions in inorganic nature. The 

 mechanists analyze many of the so-called instinctive perform- 

 ances of animals into rigorous taxic and tro])ic reactions to 

 specific external influences or .'.timuli. Chemotaxis, phototaxis, 



t'lG. 166.- -Regeneration in nature of starfish, Linckia. The regenerated specimens 

 rihown in the figure were collected as living animals on the coral reefs of Samoa. 

 These specimens show the great capacity for regeneration pos- essed by this star- 

 fish a portion of an arm being capable of regenerating the dis'; and all the other 

 arms. 



and oxygenotaxis, heliotropism, geotropism, thigmotro])ism, 

 etc., are the names applied to the growth or motion reactions 

 of organisms or their ])arts, conditioned by such external 

 stimuli 01 cmtrol-influences as light, gravitation, contact, the 

 piesence vi oxygon or of various other chemical substances. 

 And an account of the ingenious experimentation which has 



