50 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 



As in Astacus the abdomeu in the first stage of C. affinis, just as in some 

 other species of Cambarus studied by Faxon ('85), has only four pairs of evi- 

 dent pleopods. The sixth pair are but partly formed and enclosed within the tel- 

 son while the first pair exist here as minute buds readily overlooked and not 

 found in Astacus nor as yet described in other species of Cambarus. The four 

 e\'ident pleo]iods (fig. fi?) have equal exojiodites and endopodites in contrast to 

 the proportion found in Astacus (fig. 19). The beginnings of the first pair of 

 pleopods are but minute rounded elevations of the sternal ridge of the first 

 somite (as indicated in fig. 3; Andrews, :06), and contain a small mass of nu- 

 cleated epidermal cells. The appendages of the sixth somite are large internal 

 buds that cause the .side part of the telson to be very thick as they fill all its 

 interior on each side of the anus. As this region is very translucent each 

 pleoi)od can be seen to have a long outer and a short inner lobe (figs. 46, 47). 



The first larva is in several ways more imperfect than the same stage in 

 Astacus, and as it lives inactive and fastened to the maternal pleopods it seems 

 l)ut an extension of the embryonic period in jireparation for the second stage, 

 and not at all a self supporting organism. The second stage is made way for 

 by the gradual loosening of the cuticle of the first stage, as above noted in case 

 of the claws of the chela', and by the addition within the old cuticle of the new 

 exoskeletal structure of the second stage. This was evident in the telson of a 

 larva twenty hours after hatching, where the old cuticle was raised up the length 

 of the old telson spines and new spines had grown out across this space to enter 

 the hollows of the old spines. Later, just before the moult, the space between the 

 old and new cuticle was twice the length of the old spines, which were still 

 fastened to the remnant of the telson thread, and the new spines still projected 

 across the space into the old hollow spines. 



The moulting into the second stage took place after the first stage had lived 

 this dependent and preparatory life for about fortj^-eight hours and the larva 

 resulting had the form shown in figures 68 and 69. These second larva^ unlike 

 the second stage of Astacus did not gradually become separated from the 

 mother and live isolated, but remained again adhering to the pleopods till a 

 second moult brought them into the third stage which was the first free larval 

 form. Thus the pleopods were still covered with the crowded larva'. Figure 

 70 represents a i)leopod with only part of its load of second stage larva? as 

 many had been removed. 



In the following description it will be shown that in the second lai-va also 

 there is a peculiar temporary mechanical connection of young and parent. 



Each pleopod in life was covered as with a mass of animated jewels of 

 pink and garnet colors. The flesh-colored larva' were still strongly marked by 

 the yolk that remained in each as a garnet red mass of saddle-bag shape. No 

 longer firmly fixed by the chela^, the larva* soon reached about for firm objects to 



