POLYCH LT LARVA. 599 
setae resemble those of species B, but are slightly stouter. 
When alive, two pairs of short transparent tentacles could 
be seen close to the anterior end of the head, as in the 
other Phyllodocid larvae of this stage; these tentacles 
have completely disappeared from view now that the 
specimen is mounted. 
There is a single pair of brownish eyes, and during 
life the mouth and prototroch were bordered with opaque 
black pigment, which was also present on the ventral 
surface of the prostomium, and, more abundantly, on the 
posterior surface of the anal segment. The gut was 
purplish in colour. 
During life the cilia on this specimen were excep- 
tionally easy to distinguish. The prototroch consisted 
of two rows of cilia, those of the anterior row being 204 
in length, and those of the posterior row 100”. The 
akrotroch (Pl. III., fig. 39, A and B) was T-shaped, and 
its cilia were 20m long; at the posterior end of its median 
limb cilia 40” long were present between the shorter 
ones; they were not formed into the unpaired “ hook ”’ 
as in the larva of PAyllodocid A, but as their ends were 
beginning to macerate slightly, it is possible that they 
may normally be so arranged. The lateral pieces of the 
akrotroch curved backwards slightly, close to their 
origin, so as to pass behind a pair of well-defined 
“hooks ” of 40 cilia, and then curved forwards again 
as shown in the figure. Cilia were still present round 
the mouth, and a remnant of the telotroch remained on 
the dorsal surface of the anal segment. The neurotroch, 
however, was not present. 
McIntosh (1869) has described the early stages of the 
development of Phyllodoce maculata; he figures a third- 
day Trochophore which is almost identical with the 
Phylodocid Trochophores described above except in size, 
