NEREIS PELAGTCA. 275 



brownish-purple eyes are larger, have lenses, and a median patch of white occupies the 

 region behind the posterior pair and passes forward as a wedge in front. A brown 

 patch exists behind the posterior pair, mimicking a third pair on each side. A little 

 white also occurs to the exterior of the anterior eye. The prickles of the proboscis agree 

 with the typical form. The anterior feet, whilst also resembling those of Nereis pelagica 

 generally, have the dorsal cirri of the first seven enlarged in the middle. At the 

 seventeenth foot the changes in the lobes of the feet commence with increased vascularity, 

 and this increases in the posterior feet. The coloration above alluded to (greenish, with 

 a slight tinge of red) extends at least as far backward as the seventeenth foot, gradually 

 fading behind, all the feet being paler than the body. The dorsal blood-vessel enlivens 

 the region, and by-and-by fine, dark-greenish, granular transverse lines mark each 

 segment, but the posterior region is only granulated. A little later, as in the beginning 

 of March, those with the nuptial form as described have the sperms extending far 

 forward — in front of the region with the modified feet. The body behind the greenish 

 anterior region is pale — whitish or cream-coloured — from the sperms ; indeed, some 

 specimens are whitish up to the peristomial segment, laterally and ventrally. The tip of 

 the tail is slightly pinkish from the blood-vessels. 



These forms are likewise found in June and July under stones near low water-mark, 

 or in runlets of water at half -tide. They swim freely about in the water assisted by the 

 large lamellas. In some many of the feet are only half the size of the others, having 

 apparently either been later in assuming the change, or in process of reproduction. The 

 dense whitish mass which exudes on rupture consists of sperm-cells not yet matured. The 

 cells are not entirely granular throughout. 



In a male with typical paragnathi (Plate LII, fig. 2), procured on the 18th January, 

 the first fifteen feet are more or less normal, with the exception of the enlargement of the 

 dorsal cirrus in the first seven segments and the slight enlargement of the ventral cirrus in 

 five. The sixteenth foot has a minute flap close to the internal border of the dorsal cirrus, 

 and a like rudiment occurs in a similar position to the ventral cirrus. A rudiment of a 

 lamella also appears posteriorly at the tip of the inferior setigerous process. At the 

 seventeenth foot the three lamellae or flaps are larger, but the bristles (homogomph) are 

 unaltered. The heterogomph bristles are absent. The full development of the 

 heteronereid foot occurs in the thirty- seventh and neighbouring feet (Plate LXXI, fig. 

 7 f), in which the lamella on the ridge internal to the dorsal cirrus is fan-shaped. The 

 dorsal cirrus is rather long with nine or ten papillae on its lower border. Each papilla 

 has an opaque mass internally. The dorsal lobe is lanceolate and comparatively short, 

 the cirrus extending more than double its longer diameter beyond it. The dorsal setigerous 

 process bears only swimming bristles (Plate LXXX, fig. 25/;). The lobe beneath has a 

 short conical tip, and a heel projecting beyond its base internally. The inferior 

 setigerous process has a large fan-shaped lamella posteriorly. The bristles are of two 

 kinds in the specimen, viz., the dense fan of swimming bristles, and a few of the atokous 

 forms, both homo- and heterogomph. These in all probability would soon be shed. The 

 ventral lobe is tongue-shaped. The ventral cirrus has a fan-shaped lamella internally and 

 a pointed one externally. 



The average number of nereid feet in front of the heteronereid region seems to be 



