REGENERATION IN FUNDULUS HETEROCLITUS. 19 



one set of fish kept in the same tank and having the same fins 

 removed, the differences in the rate of renewal are so great that 

 some of the new fins may have completed half their growth 

 when others are just beginning to show definite regeneration. 

 Again, the caudal fin though obviously the most important in 

 many fish does not regenerate, perceptibly, faster than the others. 

 Finally, leaving aside the caudal it is difficult to say which fin is 

 the most important. The observations which Osburn ('06) has 

 recently made on the functions of fins seem to indicate that the 

 pectorals are more useful than the dorsals and anals while my 

 own results show that the former regenerate much slower. 

 Broussonet was probably led to his statement concerning the 

 relative rate of regeneration in different fins by his acceptance of 

 the idea of regeneration as an adaptation. A priori, the caudal 

 fin would regenerate, the most rapidly, on the hypothesis, since 

 it is the most useful. The facts as I have tried to show, do not 

 bear this out. 



At this point the question naturally arises as to the relation 

 between regeneration and liability to injury. It is true that the 

 fins, extending out from the body as they do, are subjected to 

 injury through brushing against obstructions, attacks of preda- 

 tory animals, etc. ; therefore, one might say, they acquired the 

 power to regenerate as an adaptation to these conditions. But 

 why, on the adaptation hypothesis, should the jaw regenerate 

 so readily, when it is extremely improbable that this structure 

 would ever be lost in a natural state ? From the lack of regen- 

 erative power in the operculum and eye no conclusions can be 

 drawn for or against this hypothesis, since these structures are 

 not especially liable to injury under normal conditions. The 

 power to regenerate scales, however, seems truly adaptive. 



ZOOLOGICAL LABORATORY, COLUMBIA UNIVERSITY, 

 October 6, 1906. 



LITERATURE CITED. 

 Broussonet, M. 



1786 Observations sur la regeneration de quelques parties du corps des Poissons. 



Hist, de 1'Acad. Roy. des Sciences, 1786. 

 Colucci, V. S. 



'91 Sulla regenerazione parziale dell' occhio nei Tritoni. Mem. della R. 

 Accad. delle Scienze dell' 1st. di Bologna (Ser. V.), I. 



