POLYCH MT LARVAS. 635 
that there is now a marked enlargement of the body 
immediately behind the prototroch; the cells in this 
region appear to contain large vacuoles. 
In life the cilia are arranged as shown in Pl. IV., 
fig. 40, and a pair of opaque reddish-brown eye-spots are 
present on the head (PI. IV., fig. 40). The cilia of the 
prototroch are-75 long, and are very powerful; at the 
apex, or slightly dorsal to it, is a tuft of cilia. The 
mouth is bordered by large lips, which differ from those 
of the Spioniform larvae in that they are situated entirely 
behind the prototroch, as in the larvae of Polynoé; and 
from those of the larva of Polynoé in that they close in 
the mouth laterally as well as on the anterior side. These 
lips are bordered and covered on the inner side with cilia 
20 long; and at the posterior angle of the mouth in the 
mid-ventral line there is a tuft of 40m cilia (see Pl. IV., 
fig. 47c,; showing the lips of an older larva, from which 
these measurements were actually taken). The lips are 
almost always retracted in preserved specimens, though 
the larva shown in Pl. IV., fig. 41, has died with them 
extended, and with the anterior part of the oesophagus 
protruded beyond them; the tumid posterior wall of the 
protruded oesophagus in this specimen is much vacuo- 
lated; the ridge encircling the organ probably represents 
the margin of the lips when normally extended. In life the 
lips are almost invariably held extended to an even greater 
extent than is shown in PI. 1V., fig. 40,* and give the larva 
a very characteristic appearance that is well brought out 
in Willemoes-Suhm’s figure of an advanced larva (1871: 
Pl) XXXI., fig. 11), which, however, he has neither 
identified nor described. The anus is closely surrounded 
by extremely delicate short cilia; ventral to the anus is a 
* Subsequent observations suggest that in full extension a trough- 
shaped structure is protruded beyond the lips, but on account of its extreme 
sensitiveness I have been unable to examine it very closely. 
