THE SPERM- RECEPTACLE IN CAMBARUS. 179 



One unexpected feature of the annulus of the genus Cambarus 

 is the fact that it enables one to recognize a dimorphism amongst 

 the females of some, if not all, the species. The females are 

 either right handed or left handed in the sense that the sperm- 

 pockets are so placed and bent that some females have sperm- 

 pockets which are the mirror images of the pockets of the other 

 females of the same species. Indications are that about one 

 half are of one kind and one half of the other. 



Though the sperm-receptacle is, in general terms, a median 

 structure it never lies entirely along the exact middle plane nor 

 is it exactly balanced, right and left, as are so many organs in 

 the anthropods. 



In this Cuban Cambarus we find another illustration of this 

 dimorphism expressed in the annulus of the females. Of the 

 six specimens studied, four were left and two right handed. 

 The lengths of the right-handed ones were 35 and 38 mm. ; of 

 the left handed 30, 45, 45, 48. Thus the dimorphism is prob- 

 ably not a matter of age nor something that alternates in suc- 

 cessive periods of the same female as does the dimorphism, 

 so-called, of the males of the other Cambari. The differences 

 between the two forms of females are as follows : In the left- 

 handed females the sperm-pocket lies a little to the animal's left 

 of the middle of the body, Figs, i, 5, 6, 7. In the right-handed 

 female it lies to the right, Figs. 2, 4. Moreover in the two 

 cases the pockets slope in opposite directions, so that the right- 

 handed pocket is the mirror image of the left-handed one shown 

 in Fig. 7 ; that is, it looks like that one seen through the paper 

 from the other side. The crescent-like mouths of the receptacles 

 in the left-handed females open to the right and those of the 

 other to the left, so that they are to one another as new moon 

 and old moon. 



The entire posterior lobe of the annulus is also right or left 

 handed, that is to say, in the left-handed females the most 

 prominent part of the posterior face of the annulus is slightly to 

 the right of the middle and the right side is the bigger, Figs. 

 1 5 5> 6, 7. In the right-handed females the more protuberant 

 part is on the animal's left, as in Fig. 4. 



Thus taking the species as a unit there exists a symmetrical 



