MALARIA EXPEDITION TO NIGERIA 79 
3. Muscle fibres arise from the superior surfaces of these processes, 
from a short length at their distal ends, and are directed upwards 
and forwards to be inserted into the upper surface of the first 
joint of the maxillary palpi. 
Though the stylets appear to be wholly of chitinous structure yet in 
transverse section at their point of origin (plate XVI, fig. 1) it is seen that they 
really consist of a central prolongation of the delicate tissue lining the head, encased 
in a thick chitinous envelope under which is a row of flattened cells with large deeply 
staining nuclei ; these cells which secrete chitin can be traced almost to the tips of 
the labrum-epipharynx and hypopharynx. In the maxillae and mandibles traces of 
these chitin cells are seen in sections near the tips as a central staining core. (Plate 
XV, fig. 1 and 2). It is to be remarked how the shape of the stylets serve to bind them 
together, the convexity of the one above fitting into the concavity of the one below ; 
thus forming a solid chitinous awl with which the skin is pierced. A section at the 
tip of the proboscis illustrates the fitting of the stylets with one another (plate XV, 
fig. 1). In fact if the tip of the proboscis be cut off a little above the labellae, the 
stylets fall out of their labial sheath as one piece, nor do they separate unless 
pressure be applied. A good view is obtained in this way of the saw-like edges 
of the mandibles and maxillae, the latter being below and to the outside of the 
former. 
The maxillary palpi. In Anopheles, the maxillary palpi are two long 
segmented rounded processes, thickly covered with hair and scales, lying in the resting 
condition, one on either side, on the upper surface of the labium and its enclosed stylets ; 
their tips are rounded off and end a little short of the tip of the proboscis. They are 
attached to the side of the head below on either side of the clypeus, their under 
surfaces here being in close relation to the maxillae (plate XVI, fig. 2). The basal 
joint is bulged on its upper surface ; on its under surface the chitin is thickened to 
form a ridge, which is in close relation at its proximal end to the chitinous prolongation 
of the maxillae. This joint contains muscle fibres arising from the maxillary 
prolongation ('great tendon') near its union with the maxilla, which are directed 
obliquely upwards and forwards to be inserted into the bulged upper surface. 
Each palpi contain delicate connective tissue containing large cells : a nerve, 
comparatively large, arising from the lateral surface of the infra-oesophageal ganglion, 
and numerous very small tracheae. Muscle fibres are only present in the basal joint. 
The study of the maxillary palpi with regard to shape, size and surface markings is 
of great importance in the classification of species. 
The labium or lower lip is the largest of the mouth parts and acts as a sheath 
for the stylets. It commences as a free piece in the same plane as the other mouth 
parts and is a continuation of the lower anterior part of the head below the pharynx. 
On its under convex surface it is marked off from the ventral surface of the head by 
