DIPTERA 439 



The mouth parts of the female mosquito (Fig. 325 A) in principle 

 differ from those described above only in the absence of a pseudo- 

 tracheal membrane on the labellar lobes and the more slender and 

 elongated labium. Mandibles are absent in the males, maxillae being 

 represented only by palps. The housefly Musca (Fig. 325 D, E, F) has 

 lost all piercing mechanism, mandibles being absent, maxillae only 

 being represented by the palps, and the mouth parts consist of a fold- 

 ing labium with highly developed pseudotracheal membrane on the 

 labellar lobes and prominent epi-hypopharyngeal tube. Musca feeds 

 largely on fluid matter but in the presence of soluble solid food, 

 e.g. sugar, solution is effected by regurgitating alimentary fluid on it. 

 By means of small chitinous teeth situated round the point to which 

 the pseudotracheae converge surfaces of solids can be scraped so 

 enabling enzymes in the regurgitated fluids to act rapidly. 



The tsetse fly, Glossma {Fig. 22$ B), also possesses no mandibles and 

 only the palps of the maxillae. It does, however, feed on mammalian 

 blood after piercing the skin. In this form the whole labium is rigidly 

 chitinized ; the labellar lobes, from which all traces of pseudotracheae 

 have disappeared, are small and provided with chitinous teeth which 

 make the wound. Thus a second kind of blood-sucking mechanism 

 has been evolved from a form like Musca, which only possessed 

 the faculty of sucking fluid from surfaces. 



In this order are included a large number of families of the greatest 

 economic importance. Thus, to mention a few, the Tipulidae (crane- 

 flies) are voracious root feeders in the larval state, and the Cecido- 

 myidae (gall midges) are, for the most part, plant feeders as larvae. 

 The Culicidae and Simuliidae are notorious blood suckers, the former 

 family being concerned with the transmission of malaria, yellow fever 

 and elephantiasis. The Tabanidae (gadflies) are cattle pests. Among 

 the large family Muscidae we find the cosmopolitan houseflies, blow- 

 flies and the African tsetse flies. The Oestridae are endoparasitic on 

 vertebrates in the larval state and include in their numbers the ox- 

 warble fly and horse bot fly of this country. Lastly we may mention 

 the Tachinidae, whose larvae are almost exclusively parasitic on other 

 insects. 



The larvae of Diptera are among the most specialized in the Insect 

 Kingdom. Legs have been entirely lost, and the head and spiracular 

 system have undergone varying degrees of reduction. Thus the most 

 generalized larvae are at the same time eucephalous, i.e. with complete 

 head capsule, and peripneustic , i.e. with lateral spiracles on the ab- 

 domen, e.g. Bibio (Fig. 326 D). In the most specialized forms, on the 

 other hand, we find the acephalous larva whose head capsule is entirely 

 wanting. Such acephalous larvae may be either amphipneustic, with 

 only prothoracic and posterior abdominal spiracles, or metapneustic, 



