INSECTA 187 



formed by the pharyngeal muscles, the sting remains projected and 

 serves to conduct the blood into the intestine. The pharynx is 

 prolonged posteriorly into the thin oesophagus, which leads into the 

 sac-shaped stomach, placed in the thorax. At the junction of the 

 stomach and intestine are the openings of the four Malpighian vessels, 

 and six rectal glands open into the hind-gut. Two pairs of salivary 

 glands of different form have been described, one pair being bean- 

 shaped, and one pair horse-shoe shaped. 



(3) Fleas. Unlike the bug and the louse, which are flattened 

 dorso-ventrally, the flea is very much compressed laterally ; so much 

 so, in fact, that it is almost impossible to prepare whole specimens 

 for the microscope in such a way that they may be viewed from the 

 dorsal or ventral aspect. The body-parts consist of the comparatively 

 small head, which is rounded anteriorly ; the thorax, which is divided 

 into three distinct segments; and the abdomen, which is composed 

 of ten segments. On each side of the head is a diagonal groove, and 

 these grooves receive the small, club-shaped antennae. In front of 

 them in many varieties, including that of man, are the simple eyes, 

 which appear as small, black specks. The mouth-parts are placed in 

 front of, and beneath, the head. They consist of four distinct organs : 

 (1) The long labrum or upper lip, which is grooved upon the ventral 

 surface and is termed variously epipharynx, tongue, or sting ; (2) two 

 slender mandibles, also grooved, and bearing several longitudinal rows 

 of teeth ; (3) two flat, pointed maxillae, placed at the sides, and 

 bearing four-jointed palps ; (4) the labium or under lip, the two long, 

 jointed palps of which are deeply grooved and unite to form a sheath. 

 This sheath encloses the upper lip and the mandibles, which together 

 form a slender tube. In the sucking act, the tube formed by the 

 hollowed palps of the labium divides, while the inner, or sucking, tube 

 is inserted into the epidermis; blood is pumped up by the action of 

 the well-developed pharynx muscles and flows into the intestine ; 

 while at the same time saliva, secreted by four glands situated in the 

 thorax, is conveyed into the wound,' partly by way of the hollow 

 groove in the mandibles and partly by way of the labium. The most 

 recent works upon the subject describe a pumping apparatus, into 

 which the salivary ducts of both sides open. 



The head is a homogeneous chitinous capsule, but the body 

 segments vary in places both in colour and in thickness. This 

 variation is due to the formation of plates or splints of chitinous 

 material, one of which (tergit) is placed upon the dorsal, and one 

 (sternit) upon the ventral aspect of each abdominal segment. They 

 have the appearance of U or L-shaped bands and are most clearly 

 seen upon the second to seventh segments. The median portion of 

 the splint lies upon the ventral or dorsal ridge, as the case may be, 



