NEREIS (NBREILBPAS) FITCATA. 341 



great lamella pointed externally (apex of dorsal lobe) and rounded internally, with the 

 dorsal cirrus projecting from the upper border. The setigerous lobe is amalgamated 

 with that beneath it, the bristles, which have cylindrical shafts regularly camerated, and 

 long, tapering tips, passing outward from the base in front. The second lobe is some- 

 what ovate or ovato-lanceolate. The inferior setigerous lobe is bifid, the longer and 

 smaller papilla being anterior. The superior bristles have long tapering tips delicately 

 serrated. The inferior group consists of those with long tapering tips (somewhat shorter 

 than the upper series) superiorly, then intermediate forms, and inferiorly a dense group 

 of those with short falcate tips as in the figure, the edge being beset with spines. The 

 ventral lobe is tongue-shaped, and the ventral cirrus, which extends a little beyond the 

 tip of the lobe above, arises from an eminence of its own. 



The huge superior lamella somewhat increases in size proportionally, especially in its 

 vertical diameter, from the foregoing to the fifty-seventh foot (Plate LXXIII, fig. 3 c) 

 but, except a slight increase in the size of the middle lobe, the foot does not essentially 

 alter. The apex of the dorsal lobe, however, becomes slightly more bulbous than in the 

 twenty-seventh, and about the sixty-eighth or seventieth the foot presents an opaque 

 brownish glandular aspect. This brownish glandular condition becomes more marked in 

 the succeeding segments to the tip of the tail. About the same region (seventieth foot) 

 a tendency to a similar thickening occurs in the middle lobe of the foot, and at the 

 ninety-fourth foot the brownish coloration marks the contents. The terminal segments 

 thus have a brownish touch at the tip of each of these lobes, and the middle lobe has 

 slightly increased in size. The ventral cirrus is also longer, reaching beyond the tip of 

 the ventral lobe. 



In the fully developed epitokous form both divisions of the feet glisten with the 

 swimming bristles, which have broad, sabre-shaped tips. 



Habits. — Young forms occur in large numbers in the crevices of stones and shells 

 from deep water and on Filigrana. The young thus follow a different habit from those 

 adults which become commensalistic with the hermit-crab in the shells of mollusks. 

 W. Thompson mentions one at Weymouth which constructed a free tube inside the shell of 

 the whelk. The motions of the annelid are very graceful. 



In a young example about If ins. long procured with many others on a mass of 

 Filigrana implexa near the Bell Rock, the dorsal edge of the fourth foot on the right was 

 fused with a calcareous growth, apparently of a young Gellepova, which had fixed itself 

 on the dorsum near the base of the foot, which thus by-and-by had become involved in 

 the growth. 



In sickly examples the caudal segments long retain vitality whilst the anterior region 

 is blanched in death, the opposite condition of that occurring for instance in Polydora, in 

 which the anterior region is active whilst the posterior is decayed. It is used as a bait 

 for whiting. 



This is the Nereis imbecillis (Mus. Leach) from Sandgate, Kent, in the British 

 Museum. 



The commensalistic habit of this species has not resulted in much structural change, 

 and in this respect it diverges from the Lycastis (Anoplonereis Ilerrmanni of Griard, 1 ), which 

 1 'Compt. Rend./ August 21, 1882, p. 389; and 'Ann. Nat. Hist./ ser. 5, vol. x, p. 330. 



