352 



THE AMERICAN NATURALIST 



[Vol. XL 



almost exclusively to hairs upon the pleopods and upon the sterna 

 calls for explanation. In crabs Williamson (3M Ann. Rep. 

 Fisheries Board for Scotland, 1904) has recently described special 

 hairs upon the pleopods as piercing the outer egg-case and liber- 

 ating an adhesive substance contained between the inner and 

 outer part of the egg-case. His idea is that the eggs are first 

 impaled in a row upon a hair, as upon a skewer, and subsequently 

 fastened to the hair by the collapsing of the pierced outer egg-case 

 and by the adhesive material contained within it. As Williamson 

 sought to extend this view to the lobster and other Macrura, the 

 crayfish, Cambarus, was reexamined in April, 1905, to see if this 

 view would apply here, but no evidence of such skewer action of 

 hairs was found though on the other hand no absolute refutation 

 of such a view was obtained. 



In Cambarus afjinis preserved eggs have in the ovary a case 

 about i j« in thickness as seen in optical section. When they 

 leave the enveloping cellular follicle and are laid and for at least 

 five hours afterwards, they have the same thickness of case but 

 twenty-three hours after laying the case was (observed as above) 

 2 n thick. In live eggs there is a remarkable change in elasticity 

 accompanying this change in thickness of case. While the fresh- 

 laid egg glides along like a liquid drop flattened and deformed by 

 every contact and scarcely held together by its delicate case, the 

 egg thirty-six hours afterwards is a tensely spherical ball, which, 

 dropped nine inches onto a table, rebounds five inches and con- 

 tinues to bounce up and down five or six times before coming to 

 rest. This great elasticity was noticed in Astacus eggs also, by 

 Lereboullet. Such eggs, however, are normally hung to the 

 pleopod by peculiar stalks. Each egg has its separate stalk and 

 this is of elastic material comparable to the egg-case.* When 

 this stalk was pulled out to four or five times its length, to ten 

 times the diameter of the egg, it flew back like a rubber band, as 

 soon as released. 



These stalks are not formed until a little while, 15 minutes or so, 

 after the eggs enter the abdominal chamber and at first they are 



' In a few cases an egg had two stalks with a ribbon-like connection over 

 the surface of the egg. 



