288 OLIGOCHAETA 



iV. appendiculuta, with which it has been confounded by Vaillant. A ventral view 

 of the anterior segments is given by Bousfield. 



(8) Nais josinae, Vejdovsky. 

 N. josinaej Vejdovsky, SB. Bohm. Ges. 1883, p. 218. 



Definition. Lengthy 8 mm. Dorsal setae bundles, consisting of loth capilliform and uncinate 

 setae ; ventral setae uncinate only. In anterior segments the dorsal vessel forms a network. 

 Eyes absent. Hab. — Teufelsee, Bohemia. 



This species has been carefully studied by Vejdovsky (24) ; it is impossible to say 

 whether it is or is not identical with N.fusca of Caetee and N. scotica of Johnston. 

 The worm is described by Vejdovsky as resembling a Tubifex on account of its size 

 (6-8 mm. in length, 15 mm. when dividing). The setae at once distinguish it from 

 0. elinguis, for the bifurcate setae of the dorsal bundles are sigmoid, and not straight as 

 in that species. The dorsal vessel anteriorly becomes reduced in calibre ; it gives off, in 

 the first five segments, five or six pairs of lateral branches, which form an irregular 

 network ; in the posterior segments pairs of lateral trunks (one pair to each segment) 

 with the dorsal and ventral trunks. In segments vii, viii, and ix, these vessels are shorter 

 and stouter, and form veritable hearts, comparable to those of the higher Oligochaeta. 

 The organization of the vascular system of this species places it on a higher level than 

 the other members of the genus to which it may be (in my opinion only temporarily) 

 refeiTed. A more complete knowledge of its structure may very possibly necessitate 

 the creation of a new genus for its reception. 



(9) Nais h.eterocliaeta> Benham* 



N. heterochaeta, Benham, Q. J. M. S. vol. xxxiv, 1893, p. 383. 



Definition. Length, 6 mm.; number of segments, 41. Dorsal bundles consisting of one 

 capilliform and one uncinate seta, liyes present. Vascular trunks uniting dorsal with the 

 ventral vessels of anterior segments connected successively, Hab. — England. 



This species has a remarkable vascular system, of which the following is a more 

 detailed description. The dorsal vessel divides, as usual, in the prostomium into two 

 lateral trunks, which unite in the fifth segment. The branches running from the 

 dorsal to the lateral trunks in the second segment divide, each of them, into two with 

 a separate union with the laterals. The corresponding circum oesophageal vessels of the 

 next segment give off a branch which joins the perioesophageal of the fourth segment. 



