FACTORS IN ONTOGENY 



287 



tion," as certain phases 

 of regeneration are 

 called, are the property, 

 in some degree probably, 

 of most animals. 



The significance of 

 this capacity has been 

 long recognized as of 

 much importance in our 

 conceptions of the germ 

 plasm character and dis- 

 position, but no general 

 agreement regarding it 

 has even yet been 

 reached by biologists. 

 More and better under- 

 stood facts about re- 

 generation are needed. 

 And this need it seems 

 to be the province of 

 experimental biology to 

 supply. By the carry- 

 ing on of ingeniously planned and carefully controlled series 



of experiments with re- 

 generating animals, we 

 are acquiring a great 

 mass of important data, 

 and the interpretation 

 and generalization of 

 these data is certain to 

 be accomplished in the 

 near future. 



We have space here 

 to call attention to but 

 one of the ways in which 

 an understanding of the 

 phenomena of regener- 

 ation will throw light on 



FIG. 171. Regeneration of the eye of Triton: O ne of the fundamental 

 A, Edge of iris with beginning lens; B, C, D, -,-, . , , 



later stages of same ;#, whole eve with regener- Problems in develop- 



atinglens. (After Wolff and Fischel ) ment. To those biolo- 



FIG. 170. Regeneration of the flatworm, Planaria: 

 A, Specimen cut in two as far forward as eyes, 

 regenerating two half-heads ; B, cut in two at 

 one side of middle line, smaller piece having re- 

 generated a head ; C, cut partly in two, having 

 regenerated two heads in angle ; D, another 

 that produced only a single head in the angle. 

 (After Morgan.) 



