THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 



49 



after hatching the larva opens its claws widely (fig. 50), and after some failures 

 fastens them to the egg stalk, or to the setae of the mother's pleopods. Once 

 firmly locked in the hardened secretion that makes the egg stalks and binds the 

 setae together, these larval chelae remain fast during the first stage. And even 

 after the larva has escaped from its cuticle and passed into the second stage 

 the old cuticles are left firmly hung to the mother by the cast-off chelae. 



As in Astacus the chela has at first a cutting edge set with a row of few 

 and simple spines, but when the first larva is ready to moult, the loosening of 

 the cuticle reveals the fact that each spine will be replaced by one that is ser- 

 rated (fig. 62), owing to the presence of flat plates along the posterior face of 

 the new spines. In addition the second stage will have on its claw some spines 

 not represented in the first stage and also near the tips of the claw some long, 

 simple setae in place of the blunt spines there in the first stage. This figure 

 shows that the recurved tips will be abandoned in the second stage since 

 there are already formed tips that are but slightly curved hooks, to take the 

 place of former recurved tips, one of which was broken off in this specimen. 



The chela besides being so small and weak, is inferior to that of Astacus 

 in having its gills less developed, the anterior arthrobranch being very short 

 and simple and with but few side filaments. 



In the four walking legs (figs. 63, 64, 65, 66), we find the same proportions 

 as in Astacus but the pleurobranchiss are absent and the arthrobranchijE are 

 more simple, especially the anterior ones. 



The branchial formula for the first stage is thus the same as in the adult 

 and is as follows : 



That the pleurobranch of the last thoracic somite of Astacus was absent 

 from Cambarus rusticus larvae 4 mm. long and evidently just out of the egg 

 was observed by Faxon ('85) and it is probable that no members of the genus 

 Cambarus have remnants left in the early larvae of that pleurobranch still found 

 in Astacus. 



