176 E. A. ANDREWS. 



sperm-pocket it is not a new formation, fundamentally, but only 

 a specialization of the posterior part of an annular plate. The 

 two other tubercles seem to correspond to the paired, elevations 

 met with on the anterior part of the annuli of some of the higher 

 Cambari. 



In a median, lengthwise section, Fig. 3, the posterior lobe of 

 the annulus is seen to stand out from the rest of the annulus like 

 a fungus from a tree, forming a rounded shelf. Dorsal to this 

 shelf there is a large space and the black line that represents the 

 shell coming from the head, toward the right of the observer, 

 rises up over the protuberant anterior part of the annulus, between 

 the anterior tubercles, and sweeps around a deep cavity, to 



FIG. 5. Ventral view of posterior lobe of annulus of female 45 mm. long, left 



handed, 2A. 



finally emerge over the summit of the small spine of the somite 

 of the fifth legs. This figure also shows the epidermis that 

 lines the shell and the vascular, sponge-work tissue that fills out 

 the annulus and all the adjacent region up to the nerve cord, 

 on which is represented the ganglion of the somite that bears 

 the fourth pair of legs. 



The peculiarity of this annulus is that it contains the essential, 

 sperm-receptacle in the projecting posterior lobe. 



This receptacle agrees so closely in structure with the pockets 

 that contain sperm in the higher species of Cambarus that 

 there is no doubt that it is used as a sperm-receptacle, though 

 no sperm was found in it in the five females examined. The 

 appearance of the pocket as seen in the posterior lobe of the 

 annulus made translucent, is represented in Fig. 5. The pocket 

 is an oblique slit that leads off to the observer's right as far as 



