428 ZOOLOGY SECT. 



i p ai 



an 



Sub-Class II. OLIGOCHJETA. 



Chaetopoda with the sexes united, the ovaries and testes com- 

 pact and few in number. No definite parapodia are developed 



d no cirri, and only a small number of simple setae on each 

 segment. The head is not distinct. There is no metamorphosis. 

 Mostly terrestrial or fresh-water forms. 



ORDER 1. NAIDOMORPHA. 



Small Oligochaeta with relatively few segments, with asexual 

 as well as sexual reproduction. Male genital pores on, or in front 

 of, the seventh segment. The anterior part of the body is often 

 distinguished from the rest by a difference in the form or 

 arrangement of the setae. Eye-spots are frequently present. 



ORDER 2. LUMBRICOMORPHA. 



Reproduction is only sexual. The anterior part of the body is 

 never specialised, and the setae are similar throughout (except in 

 special parts, such as the clitellum). The male genital pores are 

 behind the seventh segment. There are no eye-spots. 



Systematic Position of the Examples. 



Nereis dumerilii is one of many species of Nereis, differing from 

 one another in certain minor details of their structure such as 

 the relative length of the palpi and tentacles, the size and form of 

 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 Nereidm, to which it belongs, in having the parapodia 

 biramous, and the cirri simple, and in the presence of a series o 

 denticles in the pharynx in addition to the pair of jaws. The 

 family Nereidae differs from all the other families of the Errantia 

 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 o 

 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 o 

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

 and usually a number of denticles as well. 



There are several species of the genus Lmnbricus, 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, 



