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Transactions of the [Society. 
adapted to an aquatic life, and possessed three pairs of legs and 
ten pairs of stigmata. 
Here two pairs of air sacs for hydrostatic purposes would be 
superfluous ; also the very elegantly plumed anal fin would not 
only be unnecessary, but a hindrance to progress. These, together 
with the four branchial gills, were later developments. 
We now have our larva dependent for locomotion on three 
pairs of probably stumpy legs, as those existing on other aquatic 
forms, such as Dixa , Chironomus and Tanypus. One can readily 
appreciate that a supplementary foot on the end of a long slender 
body would be of assistance. 
The present normal position of the anal segment on C. plumi- 
cornis is in alignment with the long axis of the body, which makes 
it impossible for the larva to use the hooks as a foot. (PI. XVII., 
fig. 11.) It can still, however, when necessary, draw the segment 
down until it is almost at right angles to the rest of the body. In 
this position the retractile hooked foot could be brought into play. 
(PL XVII., fig. 12.) 
We will now refer to C. pallida, the larval form of which is 
very rarely taken owing to its habit of living in dense masses of 
pond weed. 
We were fortunate in securing two in November 1920. They 
measure 9 mm. The head (PI. XVI., fig. 13) is shorter, and the 
muscles in the head are not so robust as in G , plumicornis (PI. XVI., 
fig. 14), and, in place of the two leaf- shaped appendages in front 
of the labrum, G. pallida has two simple hairs or spines, on each 
of which, midway, and towards the ends, are a number of very 
delicate spurs. The anal segments, however, are not straight, but 
turned down almost at right angles to the body. (PI. XVII., 
fig. 16.) 
It is more than probable the leaf-shaped appendages in front 
of the labrum on C. plumicornis have developed from the simple 
hairs or spines, as shown in G. pallida. If this is so, it indicates 
that G. pallida is the older species, having its turned-down anal 
segment in a position to permit the hooked foot to be used, as in 
the case of the Tanypus larva : the hooks not now being of service 
have become obsolete, and remain tucked away in the pocket in 
the ventral side of the anal segment, only being forced out when 
the larva is in a distressed condition. 
Unfortunately when mounting the larva of C. pallida the 
Canada balsam, in running under the cover-glass, swept the plumes 
together, and the anal segment also became slightly twisted out of 
shape, as can be seen by the position of the four dorsal chitinous 
spines on the extreme tail end. 
The most striking of the organs which can be readily seen with 
a hand-lens are the four reniform or kidney-shaped air sacs located 
in pairs in the thorax and ninth segment respectively. To obtain 
