668 
.T. DAVIDSON. 
The proboscis [fr.) is formed by an evagination of the 
integument at the infra-posterior end of tlie head. It may be 
withdrawn into the body for some distance, somewhat after 
the manner of an inverted glove finger, the integument form- 
ing a sheath round it, as shown in fig. 34. I have seen t 
specimens with about a half of the beak retracted. It consists 1 
of three segments — a long proximal segment, a short middle .* 
segment, and a tapering distal segment, at the extremity of 1 
which are a few sensory hairs [s. h.). A well-defined longitu- 1 
dinal proboscis groove {1. g.), in which lie the mandibles and I 
maxillae, runs along the length of its anterior face. I 
Situated beneath the mouth is the small hypopharynx (h.) 
which supports the chitinous salivary pump (s.) and is con- ' 
tinnons with the labium (proboscis). 
The mandibles {vid.) consist of a pair of delicate, chitinous 
structures which emerge from the head, at the side of the * 
mouth, and extend along the proboscis groove. They are > 
finely pointed at the distal end. 
At their proximal ends, which are situated in the head, 
they are greatly enlarged, and each is attached to a stout 
mandibular chitinous rod (m .?•.). 
The maxillae (mx.) consist of two similar structures, being 
situated immediately posterior to the mandibles, but before 
leaving the head to enter the buccal cavity, they fuse to form 
a single seta, which lies between the mandibles in the pro- 
boscis groove. 
An elongate maxillary chitinous rod extends from the wall 
of the clypeus beneath each maxilla with which they fuse. 
At the sides of the mouth the lateral walls of the clypeus 
are produced downwards as two-lobed structures, which partly 
enclose the buccal cavity. This is shown in the series of 
transverse sections through the head (figs. 6-12). It will thus 
be seen that the labrum, labium, and these lateral lobes of the 
head form a more or less enclosed buccal cavity {b. c.) sur- 
rounding the mouth. 
I shall discuss the oral appendages in greater detail when 
describing the digestive system. 
I 
