THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBARUS 27 



The other end of the telson thread remained fast inside the egg capsule 

 (fig. 4), and this attachment is as important as the above described attach- 

 ment to the telson in making the thread of use to secure the larva from being 

 lost. How the connection of the inner membrane to the egg capsule was 

 brought about was not determined but it was existent long before the embryo 

 hatched. Embryos three days before hatching killed in Worcester's liquid and 

 soaked a week in five per' cent potash showed an outer egg capsule, an inner shell 

 and a membrane that was loose and visible over the chelae and over the deeply 

 bifid telson which already bore terminal spines. And embryos nine days be- 

 fore hatching showed the same double shell and membrane, but no telson spines. 



The telson thread is thus a thin membrane formed about the embryo and 

 early fastened by radiating fibrils (fig. 4) to the inside of the inner of the two 

 layers of the egg capsule. Later in the life of the embryo this membrane be- 

 comes also fastened to the telson by secretory activity of the terminal spines. 

 When the embryo hatches the membrane is ruptured and in part turned inside 

 out and drawn into a thread-like form, fastened at both ends. Other facts re- 

 garding the telson thread will be given below in the description of Cambarus, 

 in which it also exists. 



The passage from the first to the second larval stages was seen in some 

 larvae lying in the Bottom of a dish, and in others that had fixed themselves to 

 strings. In these the old larval skin burst open and the second larva, as it 

 were, "oozed" out backward for several minutes and its chelae and abdomen re- 

 mained longer inside the old skin but were then suddenly withdrawn. For a few 

 minutes the larva in its new stage lay stretched out straight, as if dead but then 

 flopped its abdomen, moved its legs, got upright and walked and even swam 

 backward and finally crawled up into the piles of other young in the same 

 second stage. 



While the larva in the first stage was inactive and remained always 

 fastened to the mother, the second larva was active and finally abandoned the 

 mother though for a time still associated with her. Upon casting off their first 

 larval skins the larvae in the second stage leave those skins fastened by their 

 chelae to the egg stalks on the mother's pleopods, and are free to crawl about 

 over the pleopods of the mother amongst their numerous fellow-larvae. Soon 

 these larvae descend the pleopods and make short excursions under the abdo- 

 men of the resting mother and over various parts of the mother's body, finally 

 wandering off over the bottom of the aquarium for short distances to return 

 frequently to the mother again. 



The mother thus had fastened to her pleopods a large mass of old egg stalks 

 and capsules to which were fastened the cast-off skins of the larva?, and over 

 this mass crawled the active larvae till after a few days the egg cases and cast 

 skins as well as egg stalks were found to have disappeared leaving the pie- 



