836 



THE DIPTERA 



anteriorly articulate with a transverse forked sclerite whose arms run forwards. 

 To these arms the tendons of longitudinal muscles are attached, which are 

 capable of rotating them, causing the eversion of the labellae. Farther 

 forward the two labellae are strengthened internally by dorsal and ventral 

 sclerites, while a pear-shaped axial apophysis projects forwards freely from 

 the labium. 



The ventral plate is obliquely placed, and carries — (i) five teeth; (2) nine 

 sets of petiolated blades; (3) six sets of rod-like hairs; (4) five sets of opercu- 

 late hairs; (5) six sets of bifurcated hairs; (6) an anterior dorsal fringe of 

 hairs; (7) a posterior ventral set of hairs; (8) ventral phalanges or lips with 

 ventral hairs; (9) dorsal external set of hairs; and (10) latero-external set of 

 hairs. 



Internal Anatomy. — The pharyngeal tube leads into the pharynx, whose 

 wall is formed by the chitinous fulcrum. The oesophagus, at first flattened, 

 afterwards cylindrical, passes into the thorax and opens into the ventral 

 surface of the proventriculus. At this point it is joined by the duct from the 

 crop or sucking-stomach, which is a large hollow blood-reservoir lying in the 

 abdomen. The chylific ventricle has three coils. The usual Malpighian 

 tubules, small and large intestine, and rectum are present. The salivary 

 glands resemble those of Musca and Glossina. 



Method of Biting. — Stomoxys 

 carefully inspects the skin, and 

 having selected a spot, everts 

 the labellae, and by a rotatory 

 motion cuts a hole through the 

 epidermis by means of its teeth, 

 and then, inserting the proboscis 

 into the wound, sucks the blood. 



Life-History. — ^The hf e-history 

 has been studied by Newstead, 

 who finds that the incubation 

 period of the egg is two to three 

 days, the life of the larva four- 

 teen to twenty-one days, the 

 pupal stage nine to thirteen days. 

 Fig. 428.— Head of Stomoxys making the total life-cycle 

 calcitvans : Female. twenty - five to thirty - seven 



days, but this may be consider- 

 ably prolonged by the incubation and larval stages being lengthened 

 in the absence of moisture, or the presence of a low temperature. 



The eggs are i millimetre in length, white, turning later to a 

 cream colour; coriaceous and reticulated; curved on one side and 

 straight on the other, where there is a broad deep groove, wider 

 anteriorly, where the larva escapes. The number of eggs varies 

 from forty-eight to seventy- one, and they are laid in warm dung 

 and fermenting grass. 



The larva is 11 millimetres long, and tapering, yellowish in colour, 

 with blackish mouth-parts. The segmentation is not well marked. 

 The head has two large diverging processes, which carry the four- 

 jointed antennae. The mouth is armed with a hook-like mandible, 

 which carries a ventral tooth, and is attached by means of a hypo- 

 stomal sclerite to two large cephalo-pharyngeal sclerites, in front of 



