THE SPERM-RECEPTACLE IN CAMBARUS. 



175 



on the third legs. Between the fourth legs are the flaring side 

 or wing plates, and between the fifth legs are two similar plates 

 which being set on edge show better from a posterior view, 

 Fig. 2. Between the fourth and the fifth legs is the mass of 

 three tubercles, shown enlarged in Fig. 4. Between the fifth 

 legs there is a small tubercle serially homologous with the above 

 set of three that form the annular plate. 



The structures indicated in Fig. i are fringed with setae but 

 these are represented only in Fig. 2, which is a view from 

 behind. These setae add to the difficulty mentioned by Faxon 

 and by Ortmann, of finding the annulus. 



Fig. 2 shows in the foreground the low middle plate, or 

 spine, of the sternum of the fifth legs and right and left of tha 



FIG. 4. Ventral view of annulus of female 38 mm. long, 2.90 mm., A. 



the side wings of the same somite. In the background are the 

 larger wings of the fourth leg somite and at the center the 

 tubercles. The posterior tubercle stands out free, attached 

 only along its contact with the paired tubercles, so that it can be 

 moved up and down, while the anterior tubercles are pretty 

 firmly soldered to the fused sternal mass anterior to them. The 

 sides of the anterior tubercles reach under the flaring wing 

 plates, as seen in Fig. 4, so that the entire set of tubercles has 

 the proper form and connections for an annular plate. The 

 peculiarity is that the posterior part of the annulus is set off as 

 a rounded tubercle, which is not known to be the case in any 

 other crayfish. As the posterior lobe is found to contain the 



