502 MEDICAL ENTOMOLOGY 



point where the mandibles converge to meet one another and to form the 

 food canal, the maxillae come to lie external to them, their blades be- 

 coming flattened and concave on the inner surfaces, so as to fit closely to 

 the shape of the mandibles. On each blade there is a thickened area, 

 within which there is a little cellular tissue, as in the mandible ; this 

 corresponds in position to the thin area of the mandible immediately 

 external to the salivary groove. 



At the distal end the maxilla is pointed, and is armed with a row of fine 

 recurved teeth, like those on the maxillae of the Orthorraphic Diptera ; 

 as pointed out by Landois, one maxilla is a little shorter than the other.* 



It will be seen from the above that the lumen of the food channel 

 is bounded entirely by the mandibles ; the maxillae lie throughout external 

 to them, and merely assist in supporting the channel by virtue of their 

 close approximation. The channel is not formed by the four stylets in 

 equal part, as stated by Landois. 



The method of action of the proboscis can be observed under the 



binocular microscope, or even under a hand lens, as captive bugs 



feed readily after a few days' starvation, and do not 



Mechanism of the usuall attempt to i eave the piece of cloth or filter 

 Proboscis . . 



paper on which they rest ; the proboscis is brought 



into the perpendicular position, or even points forward and downward, 

 and is applied without hesitation to the skin. The bug then remains 

 stationary for a few seconds, during which period one can, under favour- 

 able conditions, observe that the points of the piercing stylets are actually 

 entering the skin. Next it gives a few short forward thrusts, as a result 

 of which the parts are driven further in, and as this occurs the labium is 

 shortened by the approximation of its chitinous portions and the pucker- 

 ing of the membraneous folds between them ; the second and third 

 joints are bent backwards, thus exposing the sucking tube, within which 

 one can see the red tint of the blood as it flows upwards to the pharynx. 

 The distal end of the labium remains pressed against the skin. The 

 angle between the proximal and distal portions of the mandibles and 

 maxillae is increased to a right angle or thereabouts, and its position is 

 advanced, that is, the appendages as a whole are thrust out of the head. 



The method by which the mouth parts are brought into use is not 

 very clear. Evidently, as Landois pointed out, the action of the re- 

 tractor muscles will result in an increase in the angle of flexion, by press- 

 ing them against the head capsule, while the protractor muscles will, by- 

 thrusting the angle forwards till it is clear of the head capsule, allow the 

 * This is not the case in Conorhinus rubrofasciatus. 



