STUDIES ON POLYCHAT LARVA. 607 
described by Claparéde (1863, pp. 77-80, Pl. VI, figs. 1-11), 
whose figures of the special structures of the anterior end are, 
however, very incomplete. In McIntosh’s note on this larva 
they are mentioned very briefly, but not figured at all. 
A pair of lateral lips (Pl. 14, fig. 5, C.£.) close-in 
ventrally a somewhat funnel-shaped space in front of the 
true mouth (see below). This space, or “ vestibule,” as it 
may be termed, opens widely to the exterior in front on a 
level with the anterior end of the head, and ventrally by the 
space between the lips; the extent of these apertures can be 
regulated by movements of the lips. 
The vestibule is lined throughout with cilia, 25 u in length,! 
which extend over the external (i. e. ventral) surface of the 
lips as far as the prototroch; this extends as a row of 60u 
cilia down each side of the head on to the lips, where its cilia 
soon become indistinguishable from those of the ciliated area 
of the lips. At least one stout (4 thick by 45 u long) (?) sen- 
sory cilium is present on the inner side of each lip (fig. 5, C. 
st.) ; its spasmodic movements, as well as its size, distinguish 
it at once from the other cilia. 
The true mouth opens into the cesophagus from the pos- 
terior end of the vestibule ; it is often exposed to view by the 
drawing aside of the lips. A broad band of neurotrochal 
40 w cilia extends forwards across the first two segments to 
join the general ciliation of the vestibule beside the mouth. 
On the peristomial segment minute cilia extend from beside 
the neurotroch obliquely forward towards a short row of 60 pu 
cilia that is situated just below and in front of the first tuft 
of setze (fig. 5). 
On the second segment, the mid-ventral region of which is 
prolonged posteriorly, pressing back the third segment to 
! The difficulties in measuring the lengths of active cilia are often 
very great. The measurements given in this paper are simply used as 
a means of comparing, more completely than could be done by employ- 
ing exclusively the limited number of applicable adjectives of comparison, 
the various lengths of the cilia situated on different parts of the body ; 
they must not be regarded as accurate measurements. 
