492 



ANNELIDA. 



developed tentacles ; the palps, which are subdivided as in the 

 Sabelliformia, have become fused with the ventral edges of the 

 peristomium, and appear as a series of ridges on each side, carrying 

 numerous filaments. The thorax consists of five segments, the 

 notopodia of three of which are well developed, and bear strong 

 setae; dorsal cirri are present along the greater part of the body, 

 and act as gills. The worms form tubes of sand. 



Fam. Hermellidae. Sabellaria Lam. (Henrietta Sav.). 



B 



FIG. 401. Diagrammatic figure representing the organisation of Myzostoma (after v. Graff, 

 from Perrier). B mouth ; cl, clO marginal cirri ; d cloaca ; E stomach ; i branches of the 

 intestine ; N ventral nervous system ; o coelom filled with ova ; pi, p5 parapodia ; ph 

 pharynx ; R rectum ; t testis ; u female generative opening ; v suckers ; $ male opening. 



MYZOSTOMIDA.* 



The Myzoetomida, though, differing in many respects from the Polychaeta, 

 may most conveniently be treated in an appendix to that group. There are 

 two genera, Myzostoma Leuckart, and Stelechopus (parasitic on Hyocrinus) 

 von Graff. They are all parasitic on Crinoids, external for the most part 



* v. Graff., "Myzostomida," Challenger Reports, vol. x., 1884, and Supplement, 

 vol. 20, 1887. Wheeler,- Naples Mitth., 12, 1896, p. 227. 



