THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBARUS 15 



bryo slowly emerged from the egg capsule it was evidently in a very inactive, 

 helpless state, soft and unable to use its limbs, so that one might expect it to 

 drop away from the egg-shell, fall to the ground, and continue its life, if at all, 

 away from the mother. However, it is well known that young crayfish remain 

 for some time upon the abdomen of the mother, which they do not leave tilt they 

 are well able to swim and to walk. This period of interrelation between mother 

 and offspring deserves special study and we will describe more in detail than 

 has hitherto been done for any crayfish the remarkable structures used in en- 

 suring the connection of mother and young from the moment of hatching up to 

 the time of real independence and free life. 



Instead of dropping away entirely from the egg-case, each soft, helpless, 

 larva hung attached to the inside of the egg-case by a delicate thread which was 

 firmly fastened at one end to the inside of the egg-case and at the other end to 

 the telson of the larva. The soft, pink-colored larvae thus at first hung out 

 from the egg capsules like the pulps from burst grape-skins and were then pre- 

 vented from entirely falling away from their capsules by these threads, so that 

 they suggested the seeds of the "cucumber tree" dangling out of their pods. 

 As the young remained limp and helpless for some time these "telson threads," 

 as we may call them, appeared to be of great use, since without them the larvae 

 would have fallen to the bottom of the water and having lost connection with 

 the parent have had small chance of survival, lacking the protection or aeration 

 furnished by the mother. 



Such telson threads are doubtless found in the European Astacus, for in 

 a footnote added by M. Eobin to Chantran's paper ('70), we read: "J'ai pu 

 constater, a 1'aide du microscope, comme 1'a montre M. Chantran a 1'Acad- 

 emie, que les petits restent pendus sous 1 'abdomen de la mere, par 1'interme- 

 daire d'un filament hyal in, chitineux, qui s'etend d'un point de la face interne 

 de la coque de I'o3uf jusq'aux quartre filaments les plus interns de chacun des 

 lobes de la lame membraneuse mediane de 1'appendice caudal. Ce filament ex- 

 iste deja lorsque les embryons n'ont encore attaint que les trois quarts environ 

 de leur developpement avant 1'eclosion. " And the same general fact is men- 

 tioned in the report of the committee awarding the Montyon prize to Chantran 

 (C. K., 75, 1872, p. 1341). Of the above passage Huxley ('80, p. 352) says: "Is 

 this a larval coat? Rathke does not mention it and I have seen nothing of it 

 in those recently hatched young which I have had the opportunity of examin- 

 ing." 



The exact mode of attachment of this filament, or telson thread, and its 

 probable nature will be described below in connection with the "telson of the 

 larva of this American Astacus and later on in considering the like structure in 

 Cambarus. 



The size of the larva in its first stage is indicated by the following rough 



