IV. POLYZOA: ECTOPROCTA 



285 



circle of tentacles, arising from the edge of the cup, enclose the peristomial area 

 in which are both mouth and anus, and between these the excretory and re- 

 productive organs open. The space between the horseshoe-shaped intestine 

 and the body surface is filled by a parenchyma containing muscle cells, and 

 correspondingly the excretory organs are protonephridia. Urnatella* fresh- 

 water. Pedicellina,* Loxosowa, marine. 



Sub Class II. Ectoprocta. 



The Ectoprocta have a spacious, often ciliated, ccelom between the 

 alimentary canal and skin, so that these are separated and have a certain 

 amount of independence (fig. 274). On this account has arisen a pecu- 

 liar method (morphologically indefensible) of treating them as two in- 

 dividuals, polypid, the intestine and tentacles; cyst id the rest, especially 

 the body wall and skeleton. 



-en, 



FIG. 274. Flustra membranacea (after Nitsche), a single animal, a, anus; ek, 

 ectocyst; en, entocyst; /", funiculus; g, ganglion; k, collar which permits complete retrac- 

 tion; m, stomach, also dermal muscular sac; o, cesophagus. A, avicularium; B, vibracu- 

 larium of Bugula (after Claparede). 



The cystid is cup-shaped or saccular. It consists of an endocyst 

 the body wall and an ectocyst a cuticular skeleton, often strongly 

 calcified, secreted by the ectoderm. The ectocyst covers only the 

 base and side walls of the endocyst, leaving the outer end soft, thus forming 

 a sort of collar into which the tentacles and adjacent parts of the cystid 

 can be retracted. The opening thus formed in the ectocyst in many species 

 (Chilostomata) can be closed by a lid (operculum). The circle of tentacles 

 . surrounds the mouth alone, while the anus is outside near the collar. The 



