No. 545] THE BIOLOGY OF THE CRAYFISH 285 



do not recognize the females, and suggests that the differ- 

 ence from the standpoint of the crayfish between the sexes 

 is a difference of behavior, which difference is perceived 

 by muscle and touch sense. 



The passivity of the female when seized is marked in the 

 crayfish, but as I shall show in another paper, in the 

 marine crabs the female is not passive but aids in the 

 movements preliminary to conjugation. 



It is possible, though I have not at present enough 

 observations to support the theory, that in the crayfish 

 and the lobster, deposition of sperm is most effective when 

 the female has just moulted and the annulus ventralis or 

 the ventral surface, as the case may be, is clean. In crabs 

 where fertilization is internal, it is necessary that the shell 

 be soft; softness is of course of no use where the fertiliza- 

 tion is external, in fact it might be injurious; but the 

 cleanness of a new coat may facilitate the deposition of 

 the spermatophores, and the retention of the plug. 



Anatomically there should be no difficulty in crossing 

 the different species of Cambarus. It would be interesting 

 to see if spermatophores deposited by a male Astacus on 

 the shell of a female Cambarus would fertilize the eggs. 

 It is quite probable, however, that the female would not 

 leave the spermatophores on her thorax and abdomen 

 until the time of egg extrusion. 



Andrews (13) transplanted sperm receptacles of several 

 females to females of another species and the mutilated 

 females lived to lay eggs but the eggs did not develop. 

 Males would not' fill the transplanted receptacles. 

 Andrews found that conjugation between species may take 

 place to some extent, but did not succeed in any case in 

 securing sperm transfer and actual crossing of species. 



There seems to be no well-marked mating season in the 

 cold-water species, including the species on which my 

 observations were made. In the ponds, mating crayfish 

 were not found later than November 1, but in the labora- 

 tory copulation occurred at intervals during the fall, 



