286 NEREIS CULTRIFERA. 



half the depth. Externally it terminates in an acnte tip, and the slightly elongated 

 dorsal cirrus is carried so far outward on the ridge of the flattened lamella that it extends 

 considerably beyond the dorsal lobe. The upper setigerous lobe is now indistinguishable 

 in the sulcus between this and the next lobe, the reduction in the size of which makes the 

 disproportion between it and the dorsal lobe very conspicuous when contrasted with the 

 condition in the fifty-seventh foot. The inferior setigerous lobe is reduced in size, and 

 the ventral lobe is so small that it projects little beyond the tip of the former. The 

 ventral cirrus is considerably smaller, and its base less prominent, while its tip goes little 

 further than the base of the ventral lobe. 



This species is often infested in Guernsey and Herm by the crustacean parasite 

 Nereicola ovata, Keferstein, 1 which generally occurs towards the posterior end of the 

 annelid, the largest example of which had about fifteen specimens, most of them, however, 

 being small. The usual number is four or five. They adhere firmly either to the groove 

 between two feet or to the sides of the feet, but they do not seem to incommode the 

 worms, and it may be supposed that the Nereis, if so inclined, can at any time remove 

 them. It is, however, by no means an active species. 



The male Nereicola (Fig. 66) is small and has a somewhat ovate carapace, which, 

 however, diminishes posteriorly. It has in front minute chitinous processes like hairs, 

 and a pair of antennules composed of four segments uniformly diminished from base to 

 apex. The edges of the last three, under pressure, have minute projections from which 

 the setaa spring. The tip of the organ has several setae which are longer than itself. 

 Behind these is a more cylindrical pair of antennas of the same number of segments, the 

 tip having five long setae, one of which surpasses the others in length. The mouth has 

 two pairs of appendages, probably representing mandibles and maxillae, the posterior 

 having its terminal process furnished with a single strong claw. Three appendages occur 

 on the ventral surface of the carapace behind the foregoing, the first two being biramous 

 limbs attached to a basal process, the third a rudimentary one in the form of a simple 

 process. The testes form a pair of symmetrical organs posteriorly, the narrowed region 

 behind being terminated by two styles. 



The young female (Fig. 68) has an ovoid outline, with a blunt anterior and a narrower 

 posterior region, and both antennae and caudal styles are visible from the dorsal surface. 

 In the fully developed condition (Fig. 67) the thoracic region is greatly enlarged, so that 

 dorsally the outline is rounded ovate, with a narrower region in front, and it is only in a 

 lateral (Fig. 69) or ventral view that the snout and tail are fully seen. The antennae are 

 similar to those of the male, as also are the appendages of the mouth and the carapace 

 posteriorly. The ovisacs are attached by slender pedicles to slight prominences on each 

 side, and form cylindrical pouches filled with a vast number of ova. The same form was 

 found by Grube at St. Vaast-la-Hougue, 2 and by the author 3 in the Channel Islands. 



The segmental organ of the annelid has a trumpet with somewhat short fimbriae or 

 lobes and long cilia (Goodrich). 



1 'Zeitschr. f. wiss. Zool./ Bd. xii, p. 461, Taf. xlii, f. 1—4, 1860. 



3 Grube termed it Nereidicola ovata in his ' Notes on the Fauna of St. Vaast-la-Hougue/ and he 

 gave two good figures. 



3 ' Quart. Journ. Micros. Sci./ vol. 10, n.s., p. 89, pi. v. 



