MALARIA EXPEDITION TO NIGERIA 77 
they are concave on their inner and convex on their outer surfaces, and are 01 uniform 
thickness for the greater part- of their length, but for a short distance above their 
sharply -pointed tips they broaden, become more lance shaped and are twisted 
once upon themselves. In a transverse section at this level, they present several 
concavities into which the sides of the labrum-epipharynx, hypopharynx and maxillae 
fit (plate XV, fig. 1). Near their termination on the outer convex surfaces, lying 
along the upper edge is a row of very fine sharply pointed teeth varying in number, 
the sharp points projecting downwards. Dimmock 1 does not describe these teeth-like 
processes as occurring in the three species of Culex on which his observations were 
made. With regard to the origin of the mandibles D;mmock z says 'at the base of 
the proboscis they appear to have no muscular attachment but to lie embedded in 
the connective tissue beneath the pharynx and above the maxillae.' 
In Anopheles costalis, plate XVI, fig. 2 shews their close relation to the inner 
surface of the base of the maxillary palpi, as a straight piece of chi tin enclosing 
delicate cellular tissue. In sections further back they are difficult to trace but appear 
to come into relation with a downward projecting plate of chitin about the level of 
the anterior edge of the gena. They would thus appear to arise from chitin in the 
close neighbourhood of the groove between the clypeus and the gena. By 
tearing away the parts of the proboscis by traction at the tip with the finger nail, the 
mandibles come away with the maxillae attached to the maxillary palpi. To the 
base of each mandible a muscle is attached by a fine tendon ; the muscle arises from 
the ventral surface of that part of the chitinous exoskeleton of the head, which is 
folded inwards beneath the eyes ; the fibres are directed forward and slightly 
downwards. 
The maxillae are two stouter lancet-shaped processes of chitin, one on each 
side ; concave on their inner surface and fitting beneath the sides of the mandibles 
and the hypopharynx. On the upper and inner surface a slight distance from its 
inner edge runs a stout ridge of chitin from which the thinner portion of the maxilla 
curves upwards and outwards. The stout ridge is continued to the distal end of 
the maxilla, forming the sharp point. Some little distance from the point of the 
maxilla the thinner portion begins suddenly to shade off like the sharp edge of a 
penknife ; this surface bears on its ventral side near the outer edge fifteen to 
twenty low conical chitinous papillae. Dimmock 3 refers to them as being on the 
dorsal surface in Culex, and says ' they are true papillae, not points of a serrate edge.' 
The thinner portion of the shaft of the maxilla is marked with alternate light and 
dark bands at right angles to its longitudinal chitinous rod ; this is due to the fine 
corrugation of its surface pointed out by Dimmock. 4 This appearance is not 
1. Dimmock, The Anatomy of the Mouth parts, etc., of some Diptera. Boston, 1 8 S I 
2. Dimmock, Loco-cit, p. 16. 
3. Dimmock, Loco tit., p. 17. 
4. Dimmock, Loco tit., p. 16. 
