456 ZOOLOGY SECT- 



the eyes, the shape of the parapodia, the form of the setae, and the 

 like. The genus Nereis differs from the other genera of the family 

 Nereidce, to which it belongs, in having the parapodia biramous 

 and the cirri simple, and in the presence of a series of denticles 

 in the buccal cavity in addition to the pair of jaws. The family 

 Nereidae differs from all the other families of the sub-order Nereidi- 

 formia of the Phanerocephala in the union of the following 

 characters : The body is always elongated and made up of a 

 considerable number of segments. The prostomium is well developed, 

 and bears a pair of tentacles, a pair of palpi, and four eyes. The 

 peristomium is devoid of parapodia, and has four pairs of tentacles. 

 The parapodia are either uniramous or biramous ; both dorsal and 

 ventral cirri are present ; the setae are compound (articulated). 

 There is a pair of anal cirri. In the pharynx there is always a 

 pair of horny jaws, and usually a number of denticles in the buccal 

 cavity. 



The members of the sub-order Nereidiformia are all character- 

 ised by the possession of well-developed tentacles and palpi, and 

 usually peristomial cirri. There are highly developed parapodia 

 with acicula, jointed setae, and dorsal and ventral cirri. The buccal 

 region of the enteric canal is eversible as a proboscis, and there are 

 usually horny jaws. 



There are several species of the genus Lumbricus, differing from 

 one another in the general form of the body, the number of the 

 segments, the shape of the prostomial lobe, and other minor 

 points. All of them agree in the presence of the following features, 

 which characterise the genus and distinguish it from the many 

 other genera of the family Lumbricidce : 



The prostomium is dovetailed completely into the peristomium. 

 The setae are always in couples. There are longer and straighter 

 setae on the clitellum. The male apertures are always on the 

 fifteenth segment. There are three pairs of vesiculae seminales, 

 in the ninth, eleventh, and twelfth segments, connected across the 

 middle line in the tenth and eleventh by sacs enclosing the ciliated 

 funnels. There are two pairs of receptacula seminis always situated 

 in the ninth and tenth segments. 



The family Lumbricidae is distinguished from the other families 

 of the sub-order Megadrili, which comprises all the Earthworms, 

 by the combination of the following features : 



The clitellum usually begins behind the twentieth segment and 

 occupies from six to nine segments ; it is incomplete ventrally. 

 Dorsal pores are present. The setae on the clitellum differ from 

 the others. The male apertures are not situated further back than 

 the fifteenth segment. There are three or four pairs of vesiculae 

 seminales, in the ninth to the twelfth segments. The testes and 

 ciliated funnels are usually in the tenth and eleventh segments ; 

 the female apertures on the fourteenth. 



