842 



THE DIPTERA 



The labium, or second maxilla, starts from the ventral area of 

 the head, and is first swollen to form the bulb. Anteriorly it is 

 grooved dorsally to hold the hypopharynx and the labrum, while 

 farther anteriorly it ends in the labellse. These structures (labellae) 

 are joined together in the ventral line, except 

 anteriorly, where there is a V-shaped notch, 

 while dorsally they possess teeth which 

 interlock. 



In the ventral line the chitinous floor of 

 the labium is prolonged forwards in the form 

 of a fork, in front of which is a membranous 

 area, anteriorly to which the inner wall of 

 each labellum becomes divided into dorsal, 

 median, and ventral segments. Each segment 

 is armed with a series of about ten rasps, 

 composed of some thirty minute bars, in front 

 of which are two pairs of teeth. Between the 

 bases of the anterior pairs of teeth there 

 projects a fan-shaped mass of spine-like scales. 



The segments are capable of eversion, 

 when the muscles pull backwards the external 

 walls of the labellae. In this way the teeth 

 would be brought in contact with the skin, 

 and the wound necessary for blood-sucking 

 made, probably by rotatory movements. 



Internal Anatomy.— The internal anatomy 

 has been carefully studied by Minchin, and 

 does not materially differ from that of 

 Stomoxys. 



The pharyngeal tube opens into the 

 pharynx, which is situated mainly in the 

 rostrum. Its walls are strongly chitinized, 

 forming the fulcrum. The oesophagus runs 

 upwards and then backwards to open into 

 the proven triculus, and to be continuous via- 

 a long \^entral duct with the crop, which lies 

 in the first two segments of the abdomen. 

 The chylific ventricle is narrow at first in the 

 thorax, but becomes wider in the abdomen, 

 where it coils several times. There are the usual ileum, colon, 

 rectum, and Malpighian tubules. 



The salivary glands are two long coiled tubes l3^ng first in 

 the abdomen, and then passing into the thorax, and probably 

 opening finally on the hypopharynx, though this has not yet been 

 worked out. 



Life-History. — The species of Glossina live in jungles or bush, 

 along the banks of streams or lakes. They appear to live principally 

 upon the blood derived from big game, but Koch believed that 

 G. palpalis lives on that of crocodiles, and Hodges, on that of hippo- 



FiG. 434. — Anatomy 

 OF A Tsetse-Fly. 



(After Minchin, from 

 Reports of the Royal 

 Society.) 



I, Pharynx; 2, oeso- 

 phagus; 3, proventri- 

 culus; 4, thoracic intes- 

 tine ; 5, duct of sucking- 

 stomach ; 6, saHvary 

 duct; 7, salivary gland; 

 8, sucking-stomach; 9, 

 abdominal intestine ; 

 10, rectum. 



