OLIGOCHAETA. 



493 



(M. pulvinar v. Gr., lives in the intestine). They infest the disc and arms, 

 and may be free or enclosed in globular cysts. 



They possess a soft and ciliated skin ; five pairs of ventrally placed parapodia 

 (Fig. 401), each of which bears a hooked seta and an aciculum ; four pairs of 

 laterally placed suckers ; and ten or more pairs of cirri placed on the margin of 

 the body. 



The alimentary canal consists of a protrusible pharynx, a stomach which 

 gives off the radially arranged caeca, and a rectum. The mouth is anterior 

 and ventral, and the anus posterior and ven- 

 tral (except in a few species in which one or 

 both openings may be dorsal). 



The nervous system consists of a nerve ring 

 surrounding the pharynx, slightly enlarged 

 dorsally, and ventrally continued into a large 

 ganglionic mass (Fig. 401), which represents 

 the ventral cords. 



The animals are hermaphrodite and protan- 

 drous, the testes maturing before the ovaries. 

 The testes are branched glands on each side, 

 and lead into two ducts which open laterally, 

 one on each side, just external to the third 

 parapodium. 



The ovaries are two small patches of coelomic 

 epithelium, and the eggs are dehisced into the 

 coelom, which they fill. From the coelom a 

 tube the oviduct passes dorsal to the rectum, 

 and opens either into the latter, or by a median 

 pore just dorsal to the anus. 



There are two nephridia, opening with cili- 

 ated funnels into the coelom and into the 

 rectum behind. 



Order 2. OLIGOCHAETA.* 



Hermaphrodite Chaetopoda ivithout 

 pharyngeal armature and parapodia. 

 Without tentacles and cirri, rarely with 

 branchiae. Gonads limited in number, 

 and restricted in position. The develop- 

 ment is direct. 



The OUfjochaeta comprise certain small, 

 and for the most part fresh-water worms, 

 and all the worms known as earthworms, 



FIG. 402. Lumbricus rubellus (after 

 G. Eisen). a, the whole worm ; 

 Cl clitellum. 6, the anterior end 

 from the ventral side, c, isolated 

 seta 



* E. Claparede, " Recherchcs Anatomiques sur Us Oligochaetes," Geneva, 1862. 

 F. Vejdovsky, System u. Morphologic der Oligochaeten, Prag, 1884. W. B. 

 Benham, "An attempt to classify Earthworms," Q. J. M. ,S'. , vol. 31, 1890. 

 F. E. Beddard, "A Monoyraph of the Oligochaeta," Oxford, 1895, which see for 

 literature. 



