ANATOMY 



343 



considers them homologous with the lateral organs of Capitellids ; 

 they are usually little developed in those species which live 

 inside cysts. The mouth and anus are usually ventral ; but in 

 M. glabrum the anus is dorsal, and in a few species both aper- 

 tures are carried on to the back by the great development of the 



FIG. 186. Myzostoma cirriferum. (After Lang and v. Graff.) The organs are supposed 

 to be seen by transparency. On the right side the more dorsal organs are shown, 

 and on the left, those lying more ventrally. a, Anus ; c, ten pairs of marginal cirri ; 

 f 1 to /*, the five parapodia of the left side, each with two chaetae ; , the branches 

 of the intestine on the right side ; m, mouth ; o, the opening of the oviduct (od) into 

 the rectum ; ov, the uterus or coelom, filled with eggs, occupying the spaces lietweeu 

 the lobes of the intestine ; p, the pharynx (acrecbolic introvert) lying in the 

 pharyngeal sac ; r, rectum ; *, the four " suckers " of the left side ; these, like the 

 parapodia, really lie on the ventral surface ; st, stomach ; t, the branching testis ; 

 <J, the pore of the sperm-duct. 



ventral surface. The alimentary canal is provided with a pro- 

 trusible pharynx ; the intestine is branched ; amongst its branches 

 is the coelom, packed with eggs, and functioning as a uterus 

 (usually called " ovary "). The true ovary is a small mass of 

 cells on each side, a proliferation of the coelomic epithelium 

 covering the intestinal wall. A median continuation of the 



