44 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 



probably perish but for this temporary fastening of the abdomen that tides it 

 over the weak period till it can reach up and take hold of the egg stalk as in- 

 dicated in figure 9 of the above paper. 



This attachment of the abdomen is the same phenomenon found in Astacus 

 and is brought about by a telson thread ; but as the eggs and larvae of Cambarus 

 are so much smaller and as the tip of the abdomen remains inside the egg cap- 

 sule the facts are not so readily made out and in a previous notice (Andrews, 

 :04) the telson thread was spoken of as proceeding from the anal region, though 

 further study shows it to be fastened to glandular spines of the telson edge as 

 in Astacus. 



In Cambarus affinis the tip of the abdomen is fastened by a short thread to 

 a crumpled membrane which lies inside of the spheroidal egg case and is firmly 

 fixed to the egg case on the side near the stalk. The short thread and the 

 membrane together are comparable to the long membranous thread that in 

 Astacus allows the larva to hang far down from the egg case. For conven- 

 ience we will describe the two parts of the telson thread separately. The short 

 part fastened to the abdomen remains on larvae 48 hours old though then broken 

 off from the more membranous part inside the gg case. The short part may 

 be whipped up and down in the water like a lash when the larva flaps its abdo- 

 men (fig. 50). 



At hatching, the telson (fig. 46) is a simple rounded, translucent lobe, with 

 minute spines on each side of the median plane, which formerly fastened it to 

 the telson thread. In this ventral view of a recently hatched larva the pleopods 

 of the fourth and fifth somites are seen free while the sixth somite has its pleo- 

 pods as lobes inside the telson on each side of the anus. The terminal part of 

 the telson is traversed by radiating lines which point to spines along the edge of 

 the telson. These lines are in reality rows of cells that are to make the 

 plumose setae of later larval stages and the rest of the translucent flat telson is 

 filled by a parenchymatous mass traversed by blood spaces in which float blood 

 corpuscles. 



The telson thread arising from the edge of the telson is a flat band that is 

 readily twisted and shows a striation due to fine wrinkles of the stiff chitin-like 

 material composing this very strong but thin and translucent membrane. 



Twenty hours after hatching, the telson had changed form, become more 

 quadrangular and its terminal part was somewhat three lobed (fig. 47). And as 

 the spines to which the telson thread was attached were all on the middle lobe 

 it seemed as if the pull of the telson thread might have aided in making the 

 middle region protrude as a lobe. At this time the cuticle of the larva was 

 separating from the body in preparation for the moult from the first to the sec- 

 ond stage. 



