286 OLIGOCHAETA 



LANKESTER and VEJDOVSKY. It is the largest of European Naids, measuring, according 

 to the last-named observer, 1-5 to 2 centimetres in length. A chain of four Zooids 

 measures as much as 3 cm. 



An illustration showing the natural size of the worm is given by O. F. MULLER (2, Tab. iv, 

 fig. i). In a magnified representation (2, Tab. iv, fig. 2) the characteristic transverse bands of 

 pigment, which led to OERSTED'S specific name of ' quadristriata ' are shown. A drawing by D'UDEKEM, 

 reproduced by VAILLANT in the third volume of the ' Histoire des AnneleV (PL xxiii, fig. 12), 

 shows the same feature, also recognizable in the first published illustration of the worm that by 

 ROSEL. Ophidonais serpentina is not only larger, but more opaque than other Naids, and is, therefore, 

 less easily studied. It is, therefore, doubtful whether WILLIAMS (1) really investigated this species, 

 since he speaks of 'the softness and transparence of the integuments.' 



The pharynx occupies the first four segments, being somewhat constricted in the 

 middle and dilated at the two extremities. The oesophagus has no glandular swelling 

 but passes (in the ninth segment) into the intestine ; the intestine as well as the last 

 three segments of the oesophagus, are covered with brown peritoneal cells. The dorsal 

 blood-vessel communicates with the ventral by three pairs of vascular arches as well as 

 at the anterior extremity, where it diA'ides into two branches which reunite to form 

 the ventral vessel. The two last pairs of arches, belonging to segments iii and iv, are 

 quite simple ; the first pair branch dichotomously, the branches join either one of the 

 two halves of the dorsal vessel or the single ventral trunk. This branching is evidently 

 a simplification of the conditions which occur in N. josinae (p. 288). This species has 

 been found with fully developed sexual organs in June (LANKESTEB), September, and 

 October (VEJDOVSKY). 



GERVAIS (pp. 19, 20) describes both 0. rermicularis*, and 0. serpentina, but declares that it is 

 impossible ' bien caracteriser deux especes de ces animaux ' ; above GERVAIS remarks upon having 

 taken 'plusieurs fois des Nats rermiculans ou serpentina, a Paris.' I presume, therefore, that I am 

 right in adding O. vermicularis to the list of synonyms. 



The species is figured by MULLEB, BEUGUIERE (PI. liii, figs. 1-4 [after MULLER]), 

 VEJDOVSKY (24, PL iii, figs. 14-16), VAILLANT (6, PL xxiii, fig. 12), OEKSTED (3, PL iii, 

 fig. 3), and BOUSFIELD (1, PL xxxiii, fig. 5). 



(5) Nais gracilis, LEIDY. 



N. gracilis, LEIDY, Journ. Acad. Nat. Sci. Philad. 1850, p. 43. 

 Slavina gracilis, VEJDOVSKY, Syst. u. Morph. 1884, p. 30. 

 Definition. Length, lomm.; number of segmrnis, 50 ; dorsal setae eapilliform only; those of 



1 'Nais rermicnlaris auclorum,' GERVAIS. 



