346 Prof. Miall and Mr. R. Shelford on the Structure and 
The anus opens on the ventral surface of the last 
segment. It is surrounded by about eight radiating folds, 
which together form a large circular area (fig. 2), which at 
first sight suggests a sucker, though we have no reason 
to suppose that it is ever used as such. The folds are 
continued internally for a considerable distance into the 
rectum, part of the mucous wall of which is there- 
fore ordinarily everted. The folds are capable of retrac- 
tion. 
The chitinous cuticle is unusually thick in most parts 
of the body. It is plainly divisible into two layers, an 
outer one, which is dense, shagreen-like, and composed 
of small scaly prominences; and a much thicker and 
softer inner layer, which stains readily (fig. 31). Micro- 
scopic examination of a larval skin cast during pupation 
shows that the inner cuticle is absorbed before moulting. 
Numerous long processes stand out from all surfaces of 
the body. These are grouped in dorsal, lateral and 
ventral series. 
Dorsal series (fig. 1). Segment 1 (prothorax) bears 
one pair, segments 2 and 3, each two pairs of simple 
processes. In all the succeeding segments except the 
last the arrangement is :—annulus |, no process; annulus 
2, no process; annulus 3, an unbranched process; annulus 
4, a branched process. Segment 11 has only the 
branched process, and the branch is so small that it can 
ouly be seen by close examination; it is of solid chitin, 
and forms what De Geer calls the smaller pair of anal 
hooks. 
Lateral series (figs. 1,2,4). Segment 1 bears one pair ; 
segments 2 and 3, two pairs each, the posterior being 
rudimentary ; segment 4, two unequal pairs; the other 
seoments with the exception of the last, three pairs each, 
the middle pair being the longest. Segment 11 has only 
a rudimentary lateral process. 
Ventral series (figs. 2,4). Segment 1 has no ventral 
processes, but only a few set ; segments 2 and 3 have 
each a pair of rudimentary processes near the middle 
line, and also a pair of long processes, which are almost 
as much lateral as ventral; segment 4 has a pair of rudi- 
mentary processes on annulus |, a pair of short ones on 
2, a pair of long ones, besides a short median one, on 3 ; 
segments 0-9 exhibit five ventral annuli, of which the last 
bears a short median process, while the others have only 
