52 THE YOUNG OF THE CRAYFISHES ASTACITS AND CAMBAEUS 



bears only simple spines as in the first stage (fig. 46), and these spines are not 

 divided into gronps (fig. 72), but all seem equally useless since none act as 

 glands and there is no telson thread formed in the second stage. The middle 

 lobe l)ears spines all along its edge, some sixteen on each side replacing the 

 fewer spines of the first stage (fig. 48). Passing in from each spine there is 

 still a radiating line of cells which is active in making the plumose setae which 

 we miss in this second stage but which will be expanded in the third stage. 



ft is to the larva of the above structure that the anal thread is fastened 

 and this may now be considered in connection with this telson that has jiro- 

 gressed so little beyond its first form. As seen in figure 71, the anal threfid 

 was in life a clear narrow i-iblion running from the anus a distance greater 

 than the length of the telson to be fast to a crumpled mass which proved to be 

 tiie cast-off cuticle. This thread was fast at one end inside the intestine of the 

 larva and at the other was fast to the cast cuticle by being continuous with it 

 at the edge of the cast off anal opening. In fact the anal thread is nothing more 

 nor less than the old cuticular lining of the intestine of the first larva still con- 

 tiuuoTis witli the cast-ot¥ cuticle of the abdomen and not yet entirely loosened 

 from the intestine of the second lai'va. An examination of the recently shed 

 larva showed that the cuticle of the larva had become loose all over the body 

 and some distance into the intestine, but that farther in it still adhered to the 

 epithelial lining of the intestine. 



When the larva has moulted, the old cuticle of the abdomen is found to be 

 telescoped and its old telson joined l)y a short cord to the new telson as shown 

 in figure 73 ; a. If the old cuticle is then pulled with forceps it does not break 

 loose but the thread comes out of the anus of the larva and is thus made longer, 

 as shown in figure 73 b, by a shortening and crum])ling of the intestine. There 

 is thus a posterior part of the intestine (y) in which the old cuticle is loose and 

 an anterior part (x) where it is still fast, the region ((/) being the first place 

 met with where the cuticle lining of the intestine does not pull away from the in- 

 testinal wall. Hence the region (y) is thrown into folds and the region (.r) 

 stretched and pulled bodily toward the anus when tension of the anal string 

 pulls the region (a) toward the anus. The anal thread is the loose lining of 

 the intestine as far as it is pulled out of the anus and while in origin a tubular 

 cuticle it is stretched out as a flat ribbon which seems made of clear wire-like 

 fibres, 1)ut in reality is only thrown into longitudinal folds due in part to the 

 longitudinal ridges which sections show are present in the intestine. In figure 

 74 is seen more enlarged the region of the intestine where the loosened cuticle 

 running up from the anus arrives at the region (a) where it is still fast to the 

 epithelial walls, as made out in preparations cleared in Bela ITaller's liquid. 



Though actual ecdysis was not seen, it is evident that what happens in the 

 inoultiug of tilt' first lai'va to the second stage, is that the lining of the intestine 



