2 so 



CCELHEL:\nXTHES 



or spindle-sliapetl, circular in section. Tire mouth, at the extreme 

 anterior cud, is either surrounded by a circle of tentacles (iig. 200), 

 retracted together with the anterior end of the body by internal muscles, 

 or is overhung by a dorsal preoral lobe or proboscis wliich may be several 

 times the length of the liody and forked at its tip (lig. 26S). 



Internal segmentation is also lost, septa being entirely lacking. The 

 nephridia are reduced in number, at most but three pairs being present, 

 and in some but a single unpaired organ. They are the sexual (.iucts; 

 the Chxtiferi have special excretory organs (tig. 26S, s;) covered with 

 branching canals opening to the body cavity by nephrostomes and 



.1 



Fio. :^6S. — Foiu'lliii vii'iJis. .1, fcmak- ^aftcr IIu\k-y) ; P, mak" (after SpoiifjclV r, 

 cloaca; </, rudiiuentarv interline; ,c, cxcretor_\" organ; /, iiilcsline; m, niusck's SLii']torlini; 

 inleslinc; 5, halls of spermatozoa in 5, in .4, proboscis (^'jreoral lobc^; ». single segnTci\tal 

 organ, t'unctioningasoviductit'J, nephridium with ciliated funnel serving as vas deferens. 



emptying into the intestine. These resemble somewhat the branchial 

 trees of the holothurians (infra), and hence the gephyra-a were formerly 

 supposed to briilge the gap between holothurians and anueliils, whence the 

 name {y(<tivpa, bridge). The vascular and ner\'ous systems are more 

 like those of other anneliils. The vascular system consists of a sinus 

 around the digestive tract and a dorsal and usually a ventral longitudinal 

 trunk; the nervous system of a brain, cesophageal collar, and ^■ent^al cord, 



