THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 37 



it were the chelae of other larvae, possessed well developed responses in the pres- 

 ence of flesh food. When meat was put on green ooze on the bottom of small 

 aquaria containing such larvae they showed no sign of being aware of it till in 

 contact with it when they seized it ravenously with their mouth parts and then 

 holding the mass with their chelae jerked back like a dog tearing meat from a 

 bone, so strongly as to pull off mouthfuls. When frightened away from the 

 meat, which was then placed one-third of an inch to one side of its former posi- 

 tion in the ooze, the larva returned to the place where the meat hud been and 

 seemed to masticate the ooze there and very slowly found the piece of meat 

 again as if through touch, taste, or smell and not at all by sight. 



The pugnacity of the third larvae resulted in loss of limbs and specimens 

 with legs pulled off at the "breaking joints" and also rapidly regenerating 

 there were seen. Chant ran stated that larvae of Astacus would regenerate lost 

 limbs in seventy days while the adult males required one and a half to two 

 years and the females three or four years. 



Excepting the newly expanded last abdominal appendages all of the append- 

 ages agreed with those of the second larva in most all details, but they were 

 larger. The first antenna, however, in place of the eight sense clubs of the 

 second stage, had eleven. These were placed as follows on the exopodite : four 

 in a group on the distal segment; three at the distal end and one upon the 

 middle of the under side of the penultimate segment; two at the distal end of 

 the antepenultimate segment and one at the distal end of the next segment. Just 

 as in the second stage the ear cavity was protected by a row of plumose setae 

 arching over it from its external border. 



*% 



The long filament of the antenna was often broken near the tip but contained 

 from 60 to 65 segments and some few of the terminal ones were constricted 

 about the middle as if they might divide at the next moult. 



The acicular setae of the filament were about one-half as long as the seg- 

 ment, from the distal ends of which they arose in whorls of five or six. To- 

 ward the tip of the filament these setae were much longer than in the second 

 larva. 



The mandibles, maxillae, maxillipeds, chelae, and walking legs with their gills 

 and setaj were the same as in the second stage except for increase of size. 



Upon the abdomen the pleopods also were as in the second stage, except 

 in the case of the expanded sixth pair above described. As yet no appendages 

 were seen upon the first abdominal somite but as in this Astacus no ap- 

 pendages were found there in the adult female it may be that only female larvae 

 were examined. The four pleopods of the somite anterior to the sixth still had 

 the exopodite longer than the endopodite, as was also the case in the new sixth 

 pleopods (fig. 42). In the adult this relative size of exopodite and endopodite 

 is reversed in the abdominal organs that serve as secondary reproductive organs. 



