AUTOLYTUS PROLIFER. 219 



Beneath is a bluntly-conical region, which is stiffened by a group of spines, several 

 of which are curved at the tip and spread out for supporting a web, it may be that 

 enclosing the ova. From this region the dense and long tuft of swimming-bristles 

 projects. These (Plate LXXIX, fig. 23 a) are translucent flattened bristles, which 

 increase in diameter towards the broad terminal part, which then diminishes a little, 

 and ends in a curved tip. 



These spines and bristles are moved by considerable strands of muscular fibres, a 

 conspicuous series being dorsal and another ventral. The inferior division of the foot 

 consists only of a setigerous region, which is bifid at the tip and bears a series of the 

 characteristic jointed bristles, the shafts of which are slightly curved towards the end, 

 which is bevelled to a point and serrated on each side. The terminal piece is short 

 and bifid as in the nurse-stock. Posteriorly a considerable portion of the tapering 

 caudal region is devoid of the long swimming-bristles. In addition to the long 

 swimming-bristles is the group of ordinary bristles with abruptly-dilated ends to the 

 shaft and a short bifid terminal piece. In many is also a single modified bristle in each 

 tuft, having a somewhat dilated end to the shaft and a lateral spike or process. 



The region bearing the ova is reddish and green, the former colour being chiefly 

 at the segment-junctions. The region behind the sac is greenish, then pale posteriorly. 

 The colours are similar but paler ventrally. The egg-sac, from a central constriction, 

 has the shape of an hour-glass. The region behind the long bristles varies in the 

 number of its segments — from ten to twelve or upwards (in the ovigerous examples), 

 the tip being furnished with a pair of short symmetrical styles or cirri. Other 

 specimens in the same month (March) show a larger number of segments anteriorly 

 and posteriorly to the ovigerous region and the long bristles. 



The stages reached by the embryos in the sac of the pelagic Sacconereis are 

 indicated in the following notes at different dates : 



April 19th, 1887. — Embryos in sac developed, and they swim in the water ; some have 

 three segments, other examples have four, besides head and tail (Plate LX, fig. 4), with 

 palpocils. Eyes four. Head of adult pinkish, and the eyes dark brown. Two appear 

 to be dorsal, but the pigment is closely connected with the ventral. The ventral 

 position of these eyes would certainly enable the animal to look downward. The eyes, 

 indeed, form a large double mass, the anterior looking upward and outward, the other pair 

 commanding the ventral surface. The tentacles are long and smooth. 



April 26th, 1887. — The young Autolyti have only two pairs of bristle-bundles, but the 

 feet extend further outwards and are more distinct. They have a more elongated and 

 pointed dorsal region, and a shorter and thicker ventral. The number of segments is the 

 same. A process appears on the head — probably a tentacle. 



April 27th, 1887. — Numerous females in the bottom trawl-like tow-net. Some are 

 dull yellowish or paler, others greenish. The ova thus differ in tint. 



May 9th, 1887. — The young have increased in size. The head has lost its palpocils. 

 The four eyes are still nearly in a transverse line, the two median being dorsal; the two 

 lateral are at the sides. The buccal segment has a large pharyngeal cavity. The next 

 two segments have rudimentary feet with bristle-bundles, the tips being bifid as in 

 Autolytus. The penultimate and the terminal segments have no bristles. The animal is 



