440 MEDICAL ENTOMOLOGY 



by the mandibles and epipharynx shall be closed tightly during the act of 

 sucking. 



The mandible is provided with a second joint (Plate LIV, fig. 8) 

 at its proximal end, by means of which it is articulated to the wall 

 of the head capsule in very much the same way as that in which 

 the maxilla of Tabanus is attached. This joint consists of a stout 

 rounded rod of chitin, attached to the base of the blade by its 

 expanded distal end. Its proximal end has on it a stout tubercle, 

 separated from the rod by a short neck, which is fitted into a small 

 pit of corresponding size and shape in the genal border of the head, 

 immediately internal to one of the spines of the comb. The rod is 

 thinner beyond the tubercle, and terminates in a blunt point. The 

 exact disposition of the muscles acting on the joint has not been 

 ascertained ; there is one well-defined bundle, terminating in a short 

 tendon, which is inserted into the expanded distal end of the rod. 

 Other short muscles appear to pass between the proximal end of the rod 

 and the wall of the head, while other fibres are attached to the pointed 

 internal end proximal to the tubercle. 



The method of action of the mandible is evidently very similar 

 to that of the maxilla of Tabanus. The internal rod, which corre- 

 sponds to the cardo, rotates on the articulation between the tubercle and 

 the pit in which it lies, the two forming a simple cup and ball joint. 

 The excursion will be at least through a right angle, and as the distal 

 end passes forwards it carries with it the blade, which is thus protracted 

 through the wound. 



The first maxillae (Plate LIV, fig. 4) of the flea are not cutting organs, 

 and probably do not enter the wound. They lie in a plane anterior but 



external to that of the mandibles. Each consists of two 

 The first maxillae . . 



portions, the palp and the blade, the latter being often 



referred to as the ' flap '. The blade is a stout conical piece of chitin, 

 apparently four-sided like a pyramid, and terminating in a stout elong- 

 ated point. The palp is articulated to the base of the blade on its anterior 

 and outer side, and hangs down in front of the other parts like an antenna. 

 It consists of four joints of the ordinary type, of which the second is the 

 longest, the first and fourth of about equal size, and the third the 

 smallest. Each joint has a whorl of four hairs at its distal border, the 

 second having in addition two whorls of four each in its middle, and the 

 third one whorl. The hairs at the distal end of the palp are very small. 

 The labium (Plate LIV, fig. 6) is the most posterior of the mouth parts, 

 and consists of two lateral portions, usually termed the labial palps, united 



