NEREIS LONGISSIMA. 327 



paragnatlii. Moreover, on the ventral aspect of the maxillary section, an irregular dark 

 brownish patch (IV) occurs on each side near the base of the jaws. That on the left is 

 the larger, and is distinctly horny (Plate LXI, fig. 1 b). 



The first foot (atokous form, Plate LXXIII, fig. 1) has dorsally a large cirrus which 

 extends considerably beyond the tip of the dorsal lobe. The latter forms a long and some- 

 what narrow cone. The setigerous lobe beneath appears as a short papilla in lateral view. 

 The ventral lobe has a similar outline to the dorsal, though its tip is less acute, and the 

 inferior line longer. The ventral cirrus is large and long, its tip reaching that of the 

 adjoining lobe. The bristles are apparently all furnished with tapering tips. 



At the third foot another lobe appears, probably above that which was dorsal in the 

 first foot. At the tenth (Plate LXXIII, fig. 1 a) the diminution of the dorsal and ventral 

 cirri, the presence of a superior setigerous lobe, and the increase in the inferior setigerous 

 lobe are the chief features. The dorsal lobe is somewhat smaller than the next, the 

 ventral being considerably shorter than these. The bristles (Plate LXXXI, fig. 6) of the 

 superior setigerous lobe are of one kind with long, tapering, spinous tips, but, in the 

 typical foot, amongst those of the inferior setigerous process, are some falcate bristles 

 (Plate LXXXI, fig. 6 a). These occur as rather stout bristles near the spine, and also 

 more slender forms at the ventral edge of the series. The falcate forms are not readily 

 seen in a cursory glance, and had escaped the notice of Malmgren — unless the northern 

 form differs from the British in this respect. 



Little change in the general form of the foot in the atokous condition takes place 

 posteriorly (to the one hundredth at least) except the increase of the gap between the 

 second lamella and the inferior setigerous lobe (Plate LXXIII, fig. 1 d), the diminution of 

 the dorsal and ventral cirri, and to some extent that of the ventral lobe. Toward the tip 

 of the tail, however, the cirri again become longer, and the inferior setigerous process 

 increases in size, whilst the ventral lobe is considerably less. 



The bristles throughout conform to the same type, though in the dorsal tuft a 

 differentiation very early occurs, even in the tenth foot, two or three of these having 

 stronger shafts than the others with more evident cameraa. These bristles, which have 

 tips, become gradually stronger and more deeply tinted in the posterior feet, until toward 

 the tail only two very robust bristles and one or two more slender remain in this 

 division. The bristles of the inferior setigerous process are slender throughout. 



In an example of the epitokous female, which had about one hundred and forty-seven 

 bristled segments, the feet remain of the normal pattern to the forty-seventh, on the ventral 

 border of which, close to the inner edge of the ventral cirrus, a small papilla occurs. 

 This in the forty-ninth foot projects as a narrow lamella. Simultaneously a tendency to 

 the development of a flap or lamella behind the superior setigerous process is observed, 

 and it increases in the succeeding feet until a large, fan-shaped lamella is formed. It 

 thus happens that, with the changes in the other parts of the foot, there is at the sixty- 

 seventh foot, for instance, the following arrangement (Plate LXXIII, fig. 1 c). Dorsally 

 is a large, thin, fan-shaped lamella, externally touching the comparatively short dorsal 

 cirrus. The dorsal lamella is a long, semi-translucent, and pointed triangle. The 

 superior setigerous lobe is opaque, blunt, and bifid, having a dense tuft of the swimmino* 

 bristles with the spine at the inferior edge. The next beneath is a long, pointed, 



