5G THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 



lu this seeoiul maxilliped (fig. 82) this substitution and addition of sette is 

 more pronounced but there is a noticeable retrogression in the gill which is 

 more simple, no longer having any lateral filaments. 



The third maxilliped (fig. 83) again, as compared with the first stage (fig. 

 (iO), has (|uite long acicular setie in place of blunt spines, and a few sparsely 

 plumose setje, noticeably a group at the tip of the exopodite. While the pos- 

 terior gill is longer the anterior is here also somewhat reduced. 



The chela now used as before for clinging to the mother has its tips some- 

 what recurved (fig. 84), but they are much straighter than in the more firmly 

 fixed first stage (fig. 61). There are added a few acicular set;e and the claw 

 is more like the adult in the development of rasp-like spines along its edges 

 in i)lace of the simple si^ines of the first stage which, as seen in figure 62, were 

 being replaced during the first stage by the toothed spines of the second stage. 



The four walking legs (figs. 85, 86, 87, 88) have changed chiefly in the ad- 

 dition of a few terminal set:B and of a few exopodite, thread-like set;e. 



The branchial formula is thus the same in the second as in the first stage. 



On the abdomen the four functional pairs of pleopods (fig. 89) are now long 

 and slender but very simple and not yet fringed with seta^, though the spinules 

 on the edges of the exopodite and endopodite are more numerous than in the 

 first stage. 



The appendages of the first abdominal somite exist as yet only in the form 

 of minute round knobs (fig. -4; Andrews, :06), but slightly larger than in the first 

 stage. The appendages of the sixth somite are still within the telson (fig. 71). 

 "When the larva is nearly ready to moult into a third stage these pleopods make 

 the telson protrude laterally more than in the above figure through the sub- 

 stance of the telson, allowing one to see the form both of the pleopods and their 

 set;?. AVhen they are expanded, at moulting into the third stage, these pleopods 

 have the appearance shown in figure 90. 



The second larva remained fastened to the mother for six days, appar- 

 ently eating nothing, and as the yolk-mass gradually diminished it seems 

 prol)able that the larva still subsisted upon the original supply of energy 

 taken from the ovary as yolk. Before the moult into the third stage the gas- 

 troliths became (luite conspicuous as blue areas showing through the body on 

 each side of the stomach. 



The actual moult occupied l)ut a few minutes and as usual the head-thorax 

 came out of the old shell first, then the legs were withdrawn from their cases and 

 finally a few flaps of the abdomen freed the larva completely. There being no 

 telson or anal thread this time, the larva at once left its old cuticle and climbed 

 uiion the pleopod of the mother. The increased strength and size of the larva 

 with the perfection of its limbs and caudal-fan would make the danger of being 

 lost on falling away from the egg much less than it was in the preceding stages 



