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The material at our disposal having been fixed in alcohol has not 
been in a sufficiently good condition for an accurate study of the soft 
cellular structures of the labella, e.g., the nerves. We hope eventually 
to examine these structures in detail. 
The species examined by us has been Stomoxys calcitrans, Linn, 
(the common “ stable-fly ”). caught in England. 
The proboscis of Stomoxys (fig. i), as in Glossina, consists of three 
parts: the lower lip or labium (r), the hypopharynx (6), and the upper 
lip or labrum-epipharynx ( a ). The actual length from the base of 
the bulb to the tip of the labella measures 2 4 1 min.; the dimensions 
just behind the fork are 130/x vertically and 150/i horizontally. 
The Labium (fig. 1, c) is relatively stout and thick, with the basal 
portion swollen and gradually tapering towards both the proximal and 
distal extremities, but less so basally. Externally in its entire length, 
as far as the labella. the labium is transversely and regularly striated 
or latticed, so that the edges of preparations mounted entire appear 
faintly crenulated. Scattered over t he labium art* also a number of short 
fine hairs, set on transparent spherical areas; more numerous, 
however, on either side of the dorsal groove. Immediately behind 
the fork of the labella (fig. 5, e), and articulating with it. are two 
conspicuous ventral sclerities (fig. 5, /). 
Labella (General account). While the arrangements of the parts 
in the labium is easily understood, that of the labella presents, on the 
contrary, considerable difficulty, and we must consider the structures 
in detail. I he labella are bilaterally symmetrical. They consist of 
•in external and internal wall on either side (fig. 20), separated by 
soft tissues. The two halves are at first separate, near the base the 
sides join ventrally (figs. 21, 22), but remain open dorsally. When the 
labella are in the resting position, the internal walls consist of two 
strong chitinous plates (fig. 20), which we may divide into a dorsal 
and ventral area. The dorsal half (k in all the figures) consists of a 
flat plate, which is the true plate of the labella. while the ventral half 
is highly specialized to form a series of teeth (j in all the figures) and 
other structures, which we shall consider in detail later. If we place 
our two hands back to back, the fingers will represent the ventral half 
tie teeth, etc.), while the palms back to back represent the dorsal 
ia . Further in the process of eversion the ventral half is capable 
