27O E. A. ANDREWS. 



But speculation is here very insecure and if use inheritance or 

 some law of perfection were known it would be easy to argue 

 that Cambaroides was an incipient Cambarus evolving from Asta- 

 cits. In any case the common ancestor of Cambams and Cam- 

 baroides must have been far back as it had the larger number of 

 gills and as Cambaroides has the primitive characters of a well- 

 developed flagellum on the first stylet and a muscle at the mov- 

 able joint between protopodite and endopodite. 



A diagram of the three genera would place Astacus and Cam- 

 baroides near together as having the same gill formula and as 

 lacking a sperm receptacle, while Cambarus should stand apart as 

 having a simplified gill formula and also very highly developed 

 sperm-transfer organs, including a sperm receptacle. At the 

 same time the diagram should indicate that Cambarus and Cam- 

 baroides kept together after departing from Astacits, and that 

 later Cambaroides went off in the direction of Astacits, leaving 

 Cambarus as at once the most specialized in its gills and the 

 most conservative in its retention of the very ancient crustacean 

 mode of sperm transfer by the employment of a sperm receptacle. 

 BALTIMORE, June 10, 1909. 



