792 



FRESH-WATER BIOLOGY 



forms a thin membrane, reenf orced by a pair of very strong chitinous 

 rods, each expanded into a transverse plate armed at their extremi- 

 ties with a series of about seven strong teeth. Posteriorly the lip 

 joins a sternumlike vaulted plate, carinated along the middle, and 

 placed between the bases of the first pair of maxillae. 



First antennae 

 \ Second an^enr,^e 

 \ \ Eye 



Branchial Plate of Mandible 

 ! Stomach 



Food balls 



Branchial setae 

 Intestine 



Ovary 



Second foot 

 '.. Furca 



Dorsal seta 



-Sub-terminal claw 

 Terminal claw 

 ^^^ ^'•Terminal seta 

 First foot 

 Branchial plate of maxilla 



natatory setae Labrum 



Fig. 1244. General anatomy of Cypris virens Jurine. (After Vavra.) 



The mandibles (Fig. 1245) are each composed of a chitinous elon- 

 gate body, and a well-developed pediform palp (Fig. 1 245 b^) . They 

 are located on either side of the body immediately behind the 

 base of the second antennae with its upper acuminate extremity 

 (Fig. 1245 ^2) articulated to the inner surface of the corresponding 

 valve just in front of the adductor muscle impressions, whereas 

 the lower incurved extremity is wedged in between the lips. The 

 greater part of the body (Fig. 1245 ^^) is hollowed to receive the 

 powerful adductor biting muscles. The cutting edge (Fig. 1245 b^) 

 is divided into several strong, bifurcate teeth. The palp (Fig. 

 1245 60 forms a thick, fleshy, somewhat pediform jointed stem, 

 curving downwards, and bears on its outer side a narrow plate, a 

 so-called branchial appendage (Fig. 1245 ^^) which is provided with 

 a number of plumose setae. 



