ON OUR PRESENT KNOWLEDGE OF THE CRUSTACEA. 231 



attached to tlie pereion. They are in the form of flattened cells, with five 

 to seven rigid immovable cilia starting from their contour, and with a 

 barrel-shaped projection about their middle. During the first two days 

 following the oviposition, these spermatozoids, which are very abundant 

 around the ova and in the mucus, become spherical and pale and remain 

 motionless ; in the following days they wither, and also become smaller, 

 darker, and irregular. Lastly, when, after the fixation of the ova, the 

 excess of the mucus has completely disappeared, in consequence of the 

 pressure exerted by the incessant contractions of the pleon (which takes 

 place in a variable period, of from eight to ten days after the oviposition), 

 those spermatophores which still remain attached to the plastron, consist 

 of small, white coriaceous filaments, either isolated or mutually adherent ; 

 they no longer show anything but a central cavity, in which the micro- 

 scope reveals only a few more or less withered spermatozoids. The wall 

 of these spermatophores retains its thickness, and remains, as before, 

 composed of a concrete, striated, tenacious mucus.' ' 



Incubation lasts about six months, and the hatching takes place in 

 May, June, or July. 



The first moult takes place ten days or thereabouts after exclusion ; 

 the second, third, fourth, and fifth moults take place at intervals of from 

 twenty to twenty-five days, so that the young animal changes its integu- 

 ment five times within a hundred days, corresponding to the months of 

 July, August, and September. The sixth, seventh, and eighth moalts 

 take place in the following May, .June, or July. So that there are eight 

 moults during the first year of the animal's existence : five in the second 

 year, and two in the third, of which the first takes place in June, the 

 second in September. From this time the young crayfish becomes an 

 adult. 



After this the moulting takes place once a year in females and twice in 

 males, which M. Chantran considers explains why the latter are larger 

 than the former, the growth being in proportion to the number of 

 moults. In the adult males the first moi^lt takes place in June or July, 

 and the second in August or September. The single moult of the females 

 occurs in August or September. 



To effect its moult, the animal places itself on its side ; with its head 

 and back it raises its carapace, which swings like a lid upon its hinge ; 

 then when it has thus completely disengaged the antei-ior part of the body, 

 it separates entirely from its old carapace by a sudden movement of the 

 posterior part. This operation, which lasts about ten minutes, is favoured 

 by the previous secretion of a gelatinous material between the two cara- 

 paces, which facilitates their disengagement. 



Twelve hours after the moults the legs of the crayfish are sufficiently 

 firm to pinch strongly. Twenty- four hours later they are completely 

 hardened, the dorsal surface remaining longer flexible ; but at the end of 

 forty-eight hours it has attained nearly a normal degree of consistency. 



The young animal remains attached to the pleopoda of the parent for 

 ten days after exclusion, when the first moult takes place. This is effected 

 actually under the tail of the mother, and M. C. Robin has ascertained 

 by means of the microscope, as shown by M. Chantran to the Academy, 

 that the young remain suspended beneath the pleon of the mother by 

 means of a hyaline chitinous filament, which extends frona a point of the 



' Comptes Rendus, January 15, 1872, tome Ixxiv. pp. 201-2. Ann. Xut. Hist. 4tli 

 ser. vol. 9, pp. 173-4. 



