POLYCH AT LARVA. 637 
from which fig. 43 was drawn. The large paleae 
become more conspicuous; their position relative to 
the segments is as before, the kite-shaped area which 
they occupy having diagonal measurements of 300” by 
90u. They are arranged as shown in Pl. IV., fig. 43a; 
four lie close together throughout their whole length, and 
have their distal extremities curled round the point of a 
short straight fifth spine; the sixth is very hard to dis- 
tinguish—in fact, it is very doubtful whether it is really 
present at all yet—and is therefore indicated by dotted 
lines only. This stage is the one figured by Willemoes- 
Suhm (see above), and is much more common than the 
others, whence 1t may be inferred that it marks a period 
of quiescence preparatory to metamorphosis. 
Metamorphosis .—From the fact that during 
my 1907 visit to Port Erin I only obtained a single 
specimen intermediate between the last-mentioned stage, 
and the secretion of the tube by an almost fully developed 
worm, it seemed probable that a rapid metamorphosis 
occurred at this point in the life-history. This single 
specimen is shown in PI. IV., fig. 44. The umbrella is 
much reduced in size, and appears somewhat shrunken ; 
the ciliated band is raised above the mouth on a pair of 
prominences; the oesophagus appears to be partially 
everted. The paleae have broken through the dorsal 
body-wall at about the middle of the first segment, as 
indicated by the lines of pigment-spots, the larva being 
now much broader here than in the plane of the proto- 
troch; the presence of the sixth of the paleae is still 
doubtful. Lateral to the groups of paleae a pair of short 
tentacles (80” by 15) are now to be seen (Pl. IV., fig. 
44; T.lat.). 
The scapha appears in profile as a region devoid of 
pigment and segmentation; the cilia of the telotroch are 
