Xo. 473] 



EGG-LAYING OF CRAYFISH 



353 



exceedingly delicate, soft, wide, flat bands. These are at first 

 very short and only slowly become as long as the diameter of the 

 egg, subsequently to become many times that and hard and narrow 

 and twisted. In this latter state they remain after the egg hatches 

 and connect the empty egg-case with the pleopod and are even 

 then a means of salvation for the young. 



Near the egg the stalk expands as a rounded tent, or bell-like 

 membrane the edges of which are fast to the egg-case over a 

 rounded area about one third the diameter of the egg. Optical 

 sections indicate that the stalk continues by this membrane over 

 the egg to make its thick elastic outer case while the thin inner 

 case is the only one near the egg over the area covered by the bell. 

 At this place only there seems to be a liquid separating the inner 

 case from the walls of the bell. The stalk seems hollow for some 

 distance up from the bell and one is led to infer that each egg is 

 slung in a bag the closed mouth of which, when drawn out, forms 

 the stalk. The stalk and bell look like glass, but have longitu- 

 dinal creases that simulate a fibrillation. The other end of the 

 stalk is continuous with a flat mass that binds together many of 

 the plumose hairs along the side of the pleopod. In fact, these 

 hairs seem rather completely invested in a secretion which holds 

 them all imbedded in a flat mass on each side of the pleopod while 

 from the edges of this mass hang out the egg stalks at intervals, 

 every five or six hairs having their investment continued out as a 

 free stalk for an egg. The stalks are like a fringe from a curtain 

 in which the hairs are fixed; but many stalks arise from the flat 

 sides of the curtain. 



The structure of the stalk when magnified four hundred diam- 

 eters is homogeneous on the outer surface but within is a clear 

 matrix full of vesicles about 1^ jjl in diameter and elongated in the 

 length of the stalk as if by the stretching of the matrix. When 

 broken, in its early stages, the jagged edges of the stalk round off 

 slightly as if somewhat paste-like. 



Some facts that seem to increase the difficulty of applying 

 Williamson's view to Cambarus are the following. One female 

 was found in which the sterna and pleopods of the first somite 

 were not clean and these alone had no eggs attached to their hairs 

 so that the painfully laborious process of cleansing seems necessary 



