FACTORS IN ONTOGENY 



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and even the more complex animals, have been shown 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 tropic reactions to 

 specific external influences or stimuli. Chemotaxis, phototaxis, 



FIG. 166. Regeneration in nature of starfish, Linckia. The regenerated specimens 

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

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

 fish, a portion of an arm being capable of regenerating the disk and ah 1 the other 

 arms. 



and oxygenotaxis, heliotropism, geotropism, thigmotropism, 

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

 of organisms or their parts, conditioned by such external 

 stimuli or control-influences as light, gravitation, contact, the 

 presence of oxygen or of various other chemical substances. 

 And an account of the ingenious experimentation which has 



