327] REGENERATION OF CRAYFISH APPENDAGES 7)9 



have found in the crayfish, still it was far from being typical. 

 In spite of the differences in the character of the regeneration of 

 the shrimp and crayfish, there are sufficient similarities to point 

 to a close relationship; and both instances may be regarded as 

 arguments in favor of considering the Decapod eye a modified 

 segmental appendage. Morgan's experiments upon the eyes of 

 the hermit crab should be considered as belonging to the same 

 series. But as he gives no details, I am unable to say whether 

 the regenerated structures in the crab are more nearly like those 

 regenerated by the crayfish or those regenerated by the shrimp. 

 It is possible that, if the conditions for experiment could 

 be rendered more natural and hence more favorable, many ad- 

 ditional facts could be learned which would be decisive in favor 

 of reversion or against it, but at present the question must re- 

 main an open one. 



IV. GENERAL CONSIDERATIONS. 



It IS not my intention to enter upon a detailed, theoretical 

 discussion of regeneration. The phenomena of regeneration are 

 not more explicable in the crayfish than in other animals, and at 

 present it is not theory but fact that will prove useful in the 

 ultimate solution of the problem if a solution is ever to be 

 reached. 



The points of interests to be mentioned here are to be 

 found in the similarities and dififerences between my own exper- 

 iments and those of others. For instance, in Herrick's exper- 

 iments upon the lobster, he comes to the conclusion that the 

 power of regeneration is regulated according to the uses of the 

 parts injured. He says (loc. cit., p. io7), "The power of regen- 

 erating a lost part varies in both vertebrates and invertebrates in 

 direct proportion to the physiological importance of the part, as 

 Weismann has clearlv shown." 



