207] REGENERATION OF CRAYFISH APPENDAGES I9 



organs. In the case of the other abdominal appendages, except 

 the sixth pair, regeneration, if it does take place, is very slow in 

 beginning. Morgan ('98, p. 294) showed that in the hermit 

 crab a very small percentage of these appendages regenerate, 

 and that the process is very slow in beginning. He suggests that 

 the difference between the rate of regeneration in the abdominal 

 and thoracic legs may be partly due to the diiTerence in food- 

 supply which the two sets of appendages receive. 



4. ANTENNAE. 



In regard to the regeneration of the antennae I can add lit- 

 tle to the observations of others on the lobster, the hermit crab, 

 and other Decapoda. The process is essentially the same in the 

 crayfish as has been described by Herrick ('95, p. 106) for the 

 lobster, except that, according to my observations, regeneration 

 does not take place at different levels along the flagellum. In 

 no case that has come under my notice has regeneration of the 

 flagellum taken place except from the base. In cases where only 

 a part of the flagellum had been removed, I have never observed 

 any indications of regeneration. I have never experimented, 

 however, upon very young individuals, and it may take place in 

 them. 



When the antenna is broken off at the base of the flagellum, 

 the regenerated portion first appears as a papilla or bud; then, 

 as it grows, it becomes coiled back upon itself and, after a moult, 

 assumes a normal appearance, except in size. Fig. 18, PI. I, 

 shows a dorsal view of a regenerated right antenna. No appar- 

 ent increase in size will take place until after the next moult, 

 for the new portion has already become red. 



5. GILLS AND EXOSKELETON. 



At the beginning of my work I tried a few experiments 

 upon the gills and exoskeleton. The results of these were, 



