THE MALARIAL PARASITE 177 



internal piece called the epipharynx, is median and dorsal 

 in position. One, the hypopharynx', is median and ventral 

 in position. Two pairs, corresponding to the mandibles and 

 maxillae, are lateral. The labrum + epipharynx lies, when 

 the mouth parts are at rest, between the lips of the groove of 

 the labium ; it has the form of a nearly complete tube with a 

 fissure extending along its ventral surface and its extremity 

 is produced into a sharp point. The ventral fissure of the 

 labrum and epipharynx is closed below by the hypopharynx, 

 which is a long flat chitinous blade, in shape resembling a 

 two-edged sword, and ending in a very sharp point. A distinct 

 thickened ridge, channelled by a deep groove leading into the 

 duct of the salivary gland, runs like a mid-rib down the centre 

 of the blade, and the salivary groove is continued down to the 

 extreme point of the latter. The mandibles have the form of 

 a pair of very fine chitinous rods ending in somewhat expanded 

 lancet-shaped extremities, with very finely serrated upper 

 edges. The male Anopheles has no mandibles. The maxillae 

 are somewhat broader chitinous blades with decurved pointed 

 and serrated extremities. From the bases of the maxillae 

 spring the soft four-jointed maxillary palps, which are tactile 

 in function and not used in sucking blood. 



The female Anopheles, when she settles on the skin and 

 prepares to draw blood, moves her antennae and labial palps 

 upwards out of the way of the proboscis. She feels about 

 with the bilobed extremity of the labium, and having found 

 a suitable spot pierces the skin by working the stylets to and 

 fro. The six stylets are then thrust deeply into the puncture, 

 and saliva is injected through the aperture in the hypopharynx. 

 The saliva contains a poisonous substance causing the tissues 

 adjacent to the wound to itch and swell : probably this sub- 

 stance prevents the blood from clotting as it is sucked up by 

 the mosquito. The blood passes through the tube formed 

 by the labrum + epipharynx in front and the hypopharynx 

 behind into the mouth. The labium does not penetrate the 

 wound but rests on the surface at the point where the stylets 

 were thrust in and serves to direct and steady them. The 

 whole operation takes from two to three and a half minutes. 



The sporozoites of the malarial parasite accumulate, in a 

 manner which will be described presently, in the salivary 

 glands of the mosquito, and a number of them are injected 

 II 



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