DESCRIPTIONS OF GENERA AND SPECIES 295 



anterior to the fifth. These points distinguish it from all other genera of Naidomoi-pha. 

 The vascular system consists of a dorsal and ventral vessel which run to the end of 

 the body. In segments ii-iv they are joined by three pairs of circular vessels, which 

 are branched, and, according to Bourne's figure (5, fig. a), form a network comparable 

 to that of N. Josinae, or perhaps more like that of N. heterochaeta ; but there is no 

 irregularity in the origin of the circular vessels, and there are fewer pairs of them. 

 In segments v-vii the dorsal and ventral trunks communicate by means of unbranched 

 circular vessels. Bourne records the interesting fact that in the young buds com- 

 missural vessels occur in all the segments. 



The absence of nephridia is, if confirmed, a very remarkable character. Behind 

 the pharynx occur a pair of glands which probably represent the pharyngeal glands 

 of Ifais and other genera. 



The arrangement of the sexual organs differs from that found in I^ais and in 

 Clitellio, to which genus the worm has been referred by Vaillant. They indicate, 

 however, a transition between the more typical Naids and the Tubificidae. 



As in the Naids the paired spermathecae lie in segment v, opening in front of the 

 genital setae which replace the ventral setae of this segment ; the pouches are oval 

 in form and restricted to the fifth segment. The genital setae are ' very stout, and 

 longer than the ordinary setae, and they possess a mere rudiment of the crotchet at 

 the free extremity.' The testes and ovaries lie further back than in other Naids, 

 but a segment in front of the position which they occupy in the Tubificidae. The 

 testes^, of which there are only a single pair, occupy nearly the whole of segments 

 viii and ix; each testis is continuous through the septum which separates these 

 segments — a condition which seems to be paralleled only in the case of the genus 

 Phreodrilus. The ovaries lie in the following segment — the tenth. Neither oviducts 

 nor sperm-ducts are mentioned or figured. 



(i) Uneinais littoralis (0. F. Mullee). 



Nais littoralis, O. F. Mullee, Zool. Dan. 1788, ii, p. 54. 

 ^'Paranais littoralis, Czerniavsky, Bull. Soc. Nat. Mosc, x88o, p. 311. 

 Uneinais littoralis, Levinsen, Vid. Med. 1883, p. 218. 

 Clitellio (Clitellio) arenarius, Vaillant, Annelds, p. 415. 



Definition. Frostomium Munt and rounded. Setae of segments II, III, IV longer and 

 thinner than those which follow. Ventral setae of most segments thicker and shorter 

 than dorsal setae. Hal. — Ewojae. 



• Possibly the structures called 'testes' and 'ovaries' by Boukne are sperm-sacs and egg-sacs. 



