239] REGENERATION OF CRAYFISH APPENDAGES 41 



quently and as rapidly as in C. virilis, a species in which injuries 

 often occur under normal conditions. The above facts furnish 

 additional evidence for Morgan's contention that the capacity for 

 regeneration is independent of the physiological importance of 

 the part or its liability to injury. It is true, however, that the 

 physiological importance of a part bears a certain relation to the 

 rate of regeneration, which is doubtless to be explained on the 

 ground of differences in nutritive conditions. The greater food- 

 supply of a part which exhibits a higher functional activity may 

 well account for a more rapid regeneration than in the case of a 

 part which is of less physiological importance. I have found 

 that the thoracic appendages of the crayfish, for example, regen- 

 erate more rapidly than the swimmerets. 



V. SUMMARY. 



1 . Experience has shown that the most favorable season of 

 the year to experiment upon crayfish is during late winter and 

 early spring, a short time before the moults are likely to occur; 

 also that crayfish of small or medium size afford the most favor- 

 able material for experiment. 



2. The age of the individual, the season of the year and 

 the length of time the crayfish has been kept in confinement be- 

 fore being operated upon influence the results. Crayfish that 

 have been brought in recently should always be used. The in- 

 active life, which they necessarily lead in the laboratory, lowers 

 their vitality and consequently reduces the chances of success. 



3. Regeneration of the chelipeds normally takes place from 

 the distal surface of the second joint; it may occur, however, 

 from a higher level, but it has never been definitely proved that 

 it takes place from a lower level. Nomially, the appendage ap- 

 pears on the exterior but it may be developed within the old 

 stump. 



