VERMES 



133 



5500 meters. One valve of the shell covers the dorsal side 

 of the body and the other the ventral, and from what we may call 

 the posterior end of the ventral valve a longer or shorter stalk, 

 the peduncle, generally projects and serves as an organ ol 

 attachment. The two valves are connected near their posterior 

 ends by muscles, some serving to close, others to open them, and 

 there is often a hinge. The body of the animal lies in the pos- 

 terior part of the shell, and folds from the body-wall extend 

 forward, forming a complete membranous lining to the shell. 



iph 



at 



hi 



Fig. 123. Magellania lenticularis. Sagittal section, i.e. vertical-longitudinal, d gl, diges- 

 tive gland; d.m, dorsal mantle-lobe; d.v, dorsal valve of shell; gon l ,gorfi, gonads; ///, 

 heart; nit, intestine; Ip, lp' , lip; Iph, lophophore ; Iph', its coiled process; nith, mouth; 

 nph, nephridium; pd, peduncle; pi. si, pallial sinus ; s, setae; v.m, ventral lobe of mai 

 V.v, ventral valve of shell. (After Parker and Haswell.) 



These folds constitute the mantle, and so the free space within 

 the shell is called the mantle-cavity. In some Brachiopoda the 

 edges of the mantle are provided with short bristles or setae, 

 which are important because they occur in only one other group 

 of worms, the Annelida. 



In the mantle-cavity is the more or less horseshoe-shaped 

 lophophore, bearing ciliated tentacles, which is attached near 

 the mouth, just as in the other Molluscoidea. Often the lopho- 

 phore becomes very long and is extended into two arms, which 

 are spirally coiled (Fig. 123); these generally are confined within 



