THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 47 



would represent it as casting off a membrane at hatching which is fastened as 

 in Astacus but lacks the tubular coverings for the limbs. Here again the small 

 size of Cambarus may have led to misinterpretation of what is plain in As- 

 tacus. 



Having described this temporary, mechanical association of parent and 

 young we will next consider the more active association that lasts during the 

 rest of the first larval period. 



The larvae, supported for a time by the telson thread, soon established 

 a second connection with the mother by seizing hold of the egg case, the egg 

 stalk, or in many cases the matted pleopod setae, with their chelae, and thus, for 

 a time, were fastened both by the telson thread and by the chelae. While the 

 eggs hung loosely from the pleopod, figure 45, the young crayfish had the 

 habit of reaching in their chelae as far as possible amongst the egg stalks 

 and pulling themselves close to the pleopods so that they became densely 

 crowded together in a solid mass (fig. 52). In life this mass of young cover- 

 ing the pleopod is a curious sight suggesting mammalian young crowding for 

 maternal milk. Each held itself close to the pleopod, and when disturbed 

 drew itself all the closer as if eager to remain. The part exposed to view is 

 chiefly the rounded head-thorax which is flesh-colored but is conspicuously 

 marked by the enclosed saddle-shaped dark yolk. Here and there the legs and 

 abdomen are seen in profile (fig. 52), but generally the abdomen and legs are 

 under the body, the abdomen being bent somewhat as in a brachyuran (fig. 50) 

 and a full dorsal view shows chiefly the simple head- thorax (fig. 49). The larvae 

 thus seem egg-like, inert and inactive. 



The long-stalked egg cases stand out above the backs of the larvae as do also 

 a few belated eggs which may hatch some forty-eight hours after the rest (fig. 

 52). By this time many of the larvae have broken the telson thread and when 

 disturbed make slight movements with their legs and flap the abdomen to which 

 is fastened, like a small handkerchief, the narrow telson end of the thread, while 

 the membranous sac remains within the egg case. 



So closely do the larvae crowd together that only few of the pleopod setae 

 can be seen. Figure 52 represents a case in which some of the larvae had been 

 removed. 



While the color of the first larva is light flesh-color to the naked eye, under 

 the microscope the creature is clear, and colorless, except for the scattered, 

 arborescent, vermilion pigment cells over the carapace, abdomen, basal parts of 

 antennae and some few segments of the legs, and except for the reddish pig- 

 ment in the eyes and for the large red-brown yolk mass. 



The shape of the larva when alive is retained very well in specimens killed 

 in Worcester's liquid, though in many other liquids the head-thorax swells and 

 is abnormally glubose, while the branchiostegites roll back and expose the gills. 



