POLYCH MT LARVA. 629 . 
papillae have appeared by this time, and in addition to 
the very long setae of the first segment, somewhat 
shorter ones are present on the remaining segments with 
the exception of a few at the posterior end which never 
develop any provisional setae at all. The youngest larva 
from Port Erin is in this stage; it is probably contracted, 
and is only 1,500 in length and 150 in breadth; the 
head is rounded in front and bears a pair of tentacles 
about equal to the body in length, but only 50 in 
breadth. ‘Two regions can be recognised in the tentacles : 
a short proximal part, 100 long, which stains rather 
deeply, and a long distal part with very slight affinities 
for borax-carmine. The latter is a purely larval 
structure, and is shed after the former has reached a 
leneth of 150“, and has begun to show the characteristic 
papillate appearance of its anterior surface. These 
papillae on the permanent part of the tentacle are thick 
and fleshy, differing markedly from the spine-like 
processes that are scattered over the purely larval region. 
During this time the long provisional setae of the 
first segment reach a length of 1,000”, and many of 
those of the nine succeeding segments are shed and 
replaced by dorsal and ventral tufts of shorter permanent 
ones. These ten segments—not eight as in Claparéde’s 
larvae (loc. cit.: p. (6; Pl. X., fig. 12), or nime as in the 
adult form described by McIntosh (1878: pp. +02-3) 
form a distinct anterior region of the body. A middle 
region, composed of four (sometimes five) segments, 
retains the provisional setae for a longer period (see 
Pl, 1il., fig. 39), and crotchets instead of capillary 
setae ultimately replace them; the neuropodial crotchets 
appear before the notopodial in this region. The 
remaining segments form a posterior part of the body 
in which no provisional setae develop. At about the time 
