= a pate 
POLYCH ET LARV-E. 631 
along towards their distal ends, which extend beyond the 
posterior end of the body when held straight out, and 
even then are not as long as the setae of the first segment. 
Cuatorrerip@ (Pl. IV., figs. 12-14). 
A mesotrochal larva, probably that of Chaetopterus, 
is fairly plentiful in the Port Erin plankton during July. 
In life it is covered all over with short (10#) cilia, and 
bears first one and then two bands of longer (1004) cilia; 
the head bears three pairs of small opaque red eye-spots, 
an anterior pair placed near together on either side of 
the middle line, and two closely approximated posterior 
pairs placed one behind the other at the sides of the head. 
Long rigid cilia occur (singly ?) between the two anterior 
eyes and in other places upon the head, but their distri- 
bution is very hard to determine on account of opacity. 
The body is terminated at the posterior end by a caudal 
appendage whose shape and movements show a striking 
resemblance to the ‘‘ foot”’ of a Rotifer; this is almost 
always completely retracted in fixed specimens. 
Trochophore.—tThe youngest stages found are 
400u by 300 in size when contracted (Pl. IV., fig. 12). 
The mouth is very large, and is overhung in front by 
the broad hood-like head and bounded behind by a deeply 
cleft under-lip. It leads through a _ funnel-shaped 
oesophagus (directed backwards) into the stomach, and 
thence into a short, broad and very thin-walled rectum ; 
both these last already contain diatoms and other food- 
material from the exterior. | 
A single band of strong (100) cilia is present 
encircling the larva in the plane of the pylorus; this 
‘“mesotroch ’”’ is characteristic of larvae of the Chaetop- 
teridae. 
Metatrochophore,—A second band of power- 
