No. 447 ] BREEDING HABITS OF CRAYFISH. 



however, apparently not homoloi^ous witli ihc anmilus of ("an 

 barns but is different in i^osition and const i iu t inn Wlu'tlu 

 there may not be some kind ol arci)ta( K- ui Astac u,s. as som 

 appearances there would sii-<;\"sl. sonu'thni- more like tli 

 receptacle of the lobster, is a i)ossihilil\ that nrcds Intnrr loi 

 sideration. It is well known that the annuhis dittrrs m man 

 species of Cambarus, and now that wc know its use as a s|K'ri 



have their uses in the jiroccsscs of union. 'I lu- malr plropod 

 are also characteristically and often iemaikal)l\ diffei-ent i 

 \arious species of Cambarus. and t hcse ditleirnrt.> niav lind thci 



on the ventral side of the thorax between the sterna of th 

 somites bearini; the fourth and the fifth le-s. The sternum c 

 the former somite is a wide plate, concave across the middle lin 

 and risin- up at its ed-es^ri-ht and left as two hi-h plates tha 



at its ends against the right and left fifth legs and bearing a 

 its middle a transversely elongated rounded elexation. All thes 

 parts are hard and calcified. The annulus t^ lis all the spac 

 between the above sternal plates and thus lies across the \ entni 

 line at the interval between the fourth and the tilth legs. It i 

 close against the sternum anterior lo it and may be move( 

 slightly as if hung to it by a stiff hinge. 

 In shape the annulus. Fig. 2, is 



with i)ointed ends right and left. 



and shape near the middle - one ' ^Lmeters 



right, the other left. Between 



these elevations is a Icmgitudinal groove and at the bottom of 

 posterior part of this groove is a narrow chink into which a f 

 instrument may be forced. This chink opens i)ostenorl> mt 

 deep groove or valley that runs from right to left across i 

 major part of the annulus. This big groove is just jxjsterior 



