No. 484] ATTACHED YOUNG OF CRAYFISH 257 



and obtain a hold by them to the egg stalk or to parts of the material 

 covering the plumes of the pleopods. 



In hatching the larva escapes not only from the egg case but 

 from its loose cuticle and this cuticle, where it covers the abdomen, 

 is pulled inside out, but leaves the telson spines fast as before to 

 the inside of the cuticle over the tip of the telson. The cuticle is 

 so strong that larvjB may be picked up by the telson thread and 

 their weight does not break it even when hanging in the air. 



The attachment of the cast cuticle to the inside of the egg case 

 seems to be an indirect one; apparently the larval cast cuticle is in 

 some way fast to the egg membrane and that in turn adherent to 

 the inner of the two layers that makes the egg case, but this was 

 not definitely seen. In many eggs the embryo when young lies 

 upon the side of the egg near the stalk and we suspect some re- 

 lation between the region of fertilization and of stalk formation. 

 Later, when the embrj^o hatches, it goes out back foremost through 

 a crack in the case opposite to the stalk. In the old embryos the 

 tip of the telson is carried forward to near the eyes and not far 

 from the stalk of the egg case and in that same region of the egg is 

 found the connection of egg case to embrv'onic cuticle. Possibly 

 there may be some common factor, as gravitation, that determines 

 at fertilization the position of the embr)'o, the place for formation 

 of the egg stalk and the connection of egg case and larval cuticle. 



The ])art plav(>d by the sj)ecial telson spines in hohling the larva 

 fast to the Iclsoii tliread is shown in figures 2 and I, which show 

 how the wrinkled telson thread is connected to fihrilhir material, 

 fastened to and interlocked with the long, curved and arched 

 spines. In y)assing from the condition shown in figure 3 to that in 

 figure 4 the cuticle over the abdomen has been pulled off and 

 turned inside out and is now fn>e from the hirva except where 

 held by the Tiial.Tial fiiriii>h.Ml by the u-landnlar >},!,„... 



Whni the ycunn- -vt h..ld ..f thr nicthrr |.lcn(...ds with^ their 



fastened to th.- eg- va.v. 



In thiv lii-M lar\al ^Uvj^c ihr.r y..nM- rraxfi^h unv about 4\ mm. 

 long from tip of telson to a j)oiut between the eves where the 



