54 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 



third larva living no longer mechanically bound to the mother, with whom it 

 gradually ceases to associate. The mechanical supports, the telson thread 

 and the anal thread, are left hanging with the egg stalks, egg cases and the other 

 part of the cast off membrane and cuticle; all fast to the pleopod sete which 

 are bound together in a secreted mass. All this material soon disappears, 

 apparently being eaten up by the third larva before it leaves the mother to 

 hunt other food in wider fields. 



J 



PL 



m. 



EXPLANATION OP DIAGRAM. 



PI. = pleopod of mother; PI. H = setre of pleopod; l=cast cuticle of first larva; St. = egg stalk . 

 Sh. =egg shell; M. = membrane inside shell; Tf. = telson thread, which is broken; Af.= anal thread; 

 = second stage on the mother's pleopods held by anal thread till the claws have taken hold. 



Of the two threads which we here describe as mechanical means for pre- 

 serving the association of the mother and offspring and prolonging the ma- 

 ternal protection beyond the egg stage over larval periods that are especially 

 helpless and not self supporting, the first, the telson thread, is a secretion of 

 glands active before the larva hatches combined with an adherence of the larval 

 envelope to the egg shell that was determined very early in embryonic life. 

 The second thread, the anal thread, is a much more simple and temporary 

 attachment brought about by a delay in casting off the cuticular lining of the 

 intestine and thus utilizing what is cast off as a means of keeping the larva 

 fastened to its old cuticle till the claws can lay hold of some firm object. 



When the second larva finally becomes fastened by its claws it remains 

 some six days in a condition of. little activity. It is dependent upon the mother 

 for physical support though in a state intermediate between the invariably 

 fixed first larva and the wandering third larva. The shape of the claws (fig. 

 84) shows that they would not become as firmly locked as did the claws of the 

 first larva (figs. 61, 62), though they might stick firmly into soft material. 



