MALARIA EXPEDITION TO NIGERIA 75 
in a sharp point, and presents the appearance of the point of a pen, having a central 
split and small eye. It is composed of two conical pieces, the bases of which blend 
with the upper rounded wall of the tube — and a slight thickening at the junction of 
the two pieces in the middle line gives rise to the appearance of the slit of the pen. 
On each side of the epipharynx, at its base, and intimately blend with it, is a stout 
rod of chitin having a core of large nucleated cells ; this rod is the continuation of 
the lateral horizontal plate of chitin which at the base of the epipharynx affords 
attachment to the epipharyngeal muscles. The outer edge ot it turns gradually 
upwards and inwards, and, fusing with the lateral convex surface of the epipharynx, 
forms the lateral supporting rod of chitin described. In transverse sections the core 
of nucleated cells in its interior is seen to be continued down the whole length of the 
epipharynx and at its distal end, the core turns upwards and towards the middle line ; 
the epipharynx thus forming the extreme tip. The labrum, which is intimately 
blended with the epipharynx superiorly, thus takes no part in the formation of the 
extremity, stopping short before the nib-like tip is reached. 
The interior of the epipharynx measures at its base, dorso-ventrally 19*8 m, 
from side to side 26 /x ; at the middle of the proboscis 1 6' 5 m dorso-ventrally, 1 8 • 1 /jl 
across ; and at the middle of the labellae 13-5 m vertically by 13-2 m across. 
The labrum or upper lip is a delicate chitinous process situated immediately 
above the epipharynx and intimately connected with it, in fact it can be only partially 
separated from it by such reagents as caustic potash. For this reason Dimmock 1 
described them as one piece — the labrum-epipharynx. The labrum arises at the 
base of the clypeus and runs along the upper surface of the epipharynx. In a transverse 
section near the base of the proboscis (plate XVI, fig. 1), it is seen that the labrum is 
composed of a curved lamella of chitin with its convexity approximated to the convexity 
of the upper surface of the epipharynx. The sides of the superimposed furrow thus 
formed, lower down the proboscis, suddenly become thinned, and, turning outwards and 
downwards are thrown into folds of very delicate chitin which unite below with the 
outer edges of the lateral rods of chitin of the epipharynx (plate XVI, fig. 1), the 
space thus closed in is occupied by loose cellular very delicate connective tissue. 
Towards its distal end, the furrow of the labrum becomes shallower and opens out, 
and the labrum itself becomes more intimately fused with the epipharynx. In 
sections (plate XV, fig. 1) near the tip of the proboscis the labrum-epipharynx is seen 
as a more or less triangular-shaped piece made up of three parts ; two lateral pieces of 
chitin, in the centre of each of which is a deeply stained nucleus (chitin-cell) ; and a 
superimposed crescentic central upper piece united with the lateral portions by a very 
delicate band of tissue ; this represents the tip of the labrum, which, as has been 
already described, stops short of the end of the epipharynx. 
1. Dimmock, The anatomy of the mouth parts and of the sucking apparatus of some Diptcra. Boston, 1 88 I . P. 13. 
