THE SPERM-RECEPTACLE IN CAMBARUS. 185 



The middle plate of the eighth thoracic somite is homologous 

 with the annulus and is variously modified as a hard plale or 

 spine that may be pushed against the annulus. Probably the 

 female brings about the discharge of the sperm from the annulus 

 by use of this plate or spine, when the eggs are being laid. 

 Baltimore, March 21, 1908. 



EXPLANATION OF FIGURES. 



Drawn with camera and the Zeiss lenses indicated, reduced ^ diameters. 

 Figures 1-8, Cambarus {Procambarus) cubensis. 

 Figures 9-12, Cambarus {Paracambarus) paradoxus. 



