470 MEDICAL ENTOMOLOGY 



The function of this arrangement of rods appears to be to prevent the 

 regurgitation of the contents of the gut when the pharynx is dilated in 

 the act of sucking, and to compensate thereby for the lack of muscle in 

 the wall of the oesophagus. It is analogous, therefore, with the 

 proventriculus of Musca. Probably when the muscles of the pharynx 

 contract the negative pressure so produced first closes the lumen of the 

 proventriculus by drawing the rods in contact with one another. The 

 wall of the proventriculus itself has no muscular tissue. 



The mid-gitt is an elongate oval body, widest posteriorly, and forms by 

 far the largest part of the alimentary tract, extending to the hind end of 

 the body. Its wall consists of a layer of muscle fibres, more irregularly 

 arranged than is usually the case, and not separable into definite longitu- 

 dinal and circular bands, and internal to this a single layer of cells set 

 on a basement membrane. The cells are of the same kind as those 

 observed in the lower part of the mid-gut of Philaematomyia and other 

 Muscids. They are cubical or columnar, and present a most irregular 

 picture in most sections, many of the cells being in the act of discharging 

 their secretion into the lumen of the gut, while others have emptied 

 themselves and are degenerating. In many of the cells the nucleus is 

 situated near the lumen, and the portion of the cell containing it 

 is connected with the remainder only by a narrow neck. In other 

 parts fairly regular rows of cubical cells, with granules and some vacuoles 

 in their substance, may be found. Blood at all stages of digestion is 

 seen in fleas dissected immediately after removal from the host. 



The hind-gut is narrow, and is rather shorter than the mid-gut. It 

 lies curled up in the posterior part of the abdomen, and dilates distally 

 to form a pear-shaped rectum, in which there are six rectal papillae 

 similar to those of the Diptera. There are four Malpighian tubes, which 

 enter the gut at the posterior end of the stomach by separate openings. 



There are two pairs of salivary glands (Plate LVIII, fig. 11) on each 

 side, each two giving off fine ducts which unite after a short course to 



form a common duct, the common ducts of the two 

 The salivary glands .... . 



sides uniting in the neck and passing to the salivary 



receptacle just behind the hypopharynx. Each gland is rounded or 

 slightly oval, with the narrow end directed forward, and is composed of 

 a single layer of comparatively large cells arranged around a central 

 lumen. The common duct on each side and the distal portion of the 

 duct of each gland are provided with the familiar arrangement of 

 chitinous rings to prevent the collapse of the tube when the saliva is 

 drawn forwards by suction. 



