74 THOMPSON YATES LABORATORIES REPORT 
allowed to set until the edges of the film begin to crinkle. On placing the slide in 
water, the film comes away with the sections which are now ready for staining in situ 
in the film. Carbol-xylol must be used for clearing after dehydration. 
Most of our observations were made on Anopheles costalis, but a few specimens 
ot Anopheles maculipennis and of different species of Culex have also been examined by 
dissection. 
External anatomy of mouth parts 
The term ' proboscis ' is used to designate such of the mouth parts of 
Diptera, which taken together form their more or less flexible, shorter or longer, 
sucking apparatus. In the Culicidae the proboscis is a long slender organ arising 
from the lower projecting portion of the front of the head, beneath the clypeus or 
face. On its ventral surface it is continuous with the under surface of the head — 
the gulo-mental region. Its upper surface is sharply marked off from the clypeus 
by a deep groove. In a transverse section of the head at the base of the proboscis, 
(plate XVI, fig. 2) the latter appears to arise from a U-shaped mass under the clypeus, 
the upper parts of the arms of the U representing the genae or cheeks — narrow areas 
of the head situated in front ot the eyes. The proboscis measures as a rule about 
three or four times the length of the head; in Anopheles costalis, 2 mm. 
Parts constituting the proboscis 
The proboscis consists of the upper lip — the labrum ; the epipharynx ; these 
two being firmly united together ; the hypopharynx or tongue ; two mandibles and 
two maxillae, which are commonly known as the stylets or setae, consisting almost 
entirely ot transparent chitin, and used to pierce the skin ; and the labium, or lower 
lip, the largest and fleshy part of the proboscis, in a groove on the upper surface 
of which the other parts are ensheathed when in repose. On either side and above 
the labium are the two maxillary palps, rod-like organs, covered with hairs and scales, 
and which, in Anopheles, lie above and parallel to the other mouth parts, and extend 
almost to the tip of the proboscis. 
The general arrangement of the mouth parts to one another is seen in plate XV, 
fig. 3, a transverse section about the middle of the proboscis. 
The epipharynx. The central tube through which the blood is sucked is 
formed by the epipharynx, which is morphologically the continuation of the upper and 
lateral chitinous walls of the pharynx. This tube is tunnel-shaped, being flattened on 
its under surface ; its distal open end is oval, and looks ventrally — a fact first pointed 
out by Swammerdamm 1 in 1668. The wall of the epipharynx on the ventral surface 
becomes exceedingly thin, and fails to meet in the middle line, so that a slit is 
formed running the whole length of the epipharynx. The tip of the epipharynx ends 
1. Swammerdamm, Buck der Natur, Leipzic, 1752. 
