THE ANATOMY OF THE STYLETS OF CAMBARUS 

 AND OF ASTACUS. 



E. A. ANDREWS. 



In all the crayfishes, Cambarus and Astacus, of the northern 

 hemisphere, the limbs of the first and second segments of the 

 abdomen of the male are modified in a peculiar way and are 

 used as instruments to transfer the sperm from the defferent ducts 

 to the outside of the body of the female. These limbs we will 

 call the first and second pairs of stylets. 



In Cambarus it was found (1,2) that the stylets place the 

 sperm within a special sperm receptacle in the shell of the female. 

 In Astacus, as far as is known, the stylets deposit the sperm over 

 the shell of the female in secreted tubules, or .spermatophores. 



While the stylets are much alike in the two genera the follow- 

 ing study shows that the parts directly concerned in the passage 

 of sperm present two stages of perfection, those of Cambarus 

 being the more specialized. The first pair of stylets are firm, awl- 

 like structures, which in Astacus are evidently comparable to a 

 rolled in plate, while in Cambarus they seem solid with only 

 a superficial groove. But we now find that this groove is the 

 outlet of a concealed tubule and that in Cambarus also the organ 

 may be regarded as a modified plate. 



As the second stylets are much alike in the two genera and 

 have a subordinate role to play in the process of sperm transfer 

 we will consider chiefly the first pair. 



It is a remarkable fact that the first stylets in these cray- 

 fishes present specific differences so that the systematist relies 

 upon the forms of the stylets as an important aid in the descrip- 

 tion and identification of species. The figures of Hagen (3) and 

 of Faxon (4) show the great amount of diversity in proportion 

 and in character of termination in many species of Cambarus. 

 But despite this diversity in form the following description of the 

 first stylets in four species taken at random and representing 

 four of the six subgenera of Cambarus makes it probable that in 

 all species the stylets have the same essential anatomy and use. 



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