616 TRANSACTIONS: LIVERPOOL BIOLOGICAL SOCIBTY. 
Behind it successive segments are formed, narrow at first, 
but becoming broader as they develop; each bears a 
dorsal tuft of long (240) setae, and a ventral tuft of 
shorter ones (80), the latter appearing on each segment 
a little later than the former. The lengths of these setae 
show a steady decrease from the first segment to the 
posterior end. Gastrotrochs were seen in the living larva, 
but their precise extent was not determined. 5 
The dorsal body-wall is thin as usual, and contains 
a pair of conspicuous longitudinal muscle bands; the 
ventral wall is thicker, and even in quite small larvae 
(seven segments) shows traces of the differentiation of the 
nerve-cord which, during the development of the next 
two or three segments, becomes quite clearly defined. 
The gut, even in the earhest stages seen, contains the 
remains of unicellular organisms. No distinctive per- 
manent features have been seen in this larva, only the 
metatrochophore stage having been found. On account, 
however, of the long setae and slender body it may be 
referred with certainty to the Spioniformia. It can 
hardly be an early stage in the development of Spronid A 
because, in addition to its relatively small proportions, 
the gut always contains abundant remains of unicellular 
organisms and never the yolky (?) material there present. 
From Sprond B it is distinguished by the shortness of 
the segments relatively to their breadth; the setae, too, 
are slightly stouter and more rigid. 
Spionid D.—“ Chaetosphaera “-—(P1. IIL, figs. 36-37). 
Metatrochophore and Nectosoma.— 
This is a very large form, which is characterised by its 
tufts of strong, smooth, and slightly curved setae (Pl. I1T., 
tig. 36), and by the prolongation of the head into a snout 
which, however, is usually contracted out of all recogni- 
tion in fixed specimens (compare Pl. II1., figs. 36 and 37). 
