EXPLANATION OF PLATES VllL AND IX. 117 



pharynx near its upper end. The function of the dilatation of 

 the saHvary duct would seem to be to retain the salivary secretion. 

 When the muscles referred to contract the anterior and posterior 

 walls are separated (as in Fig. 22), and the passage is open. I 

 can scarcely think that this organ acts as a pumping mechanism 

 or syringe. 



In this chapter all essential chitinous structural fed.tures and 

 all the muscles belonging to the mouth-parts have been mentioned, 

 so that the main points of the functions of the different organs 

 can be understood. As already pointed out, the labella of Glossina 

 especially need further study (with high magnifying power), 

 which should be carried out on fresh material, or at least on 

 well-preserved spirit specimens. Moreovei*, the depth to which 

 these flies bury the proboscis in the skin of their victims should 

 be observed, as also the time occupied in biting, etc.* 



Explanation of the Figukes (Plates VIII. and IX.). 



The camera lucida was used for all the drawings, with the 

 exception of the three diagranmiatic sections of mouth-parts in 

 Glossina. Some of the figures have been drawn as seen by 

 transmitted light, and in these the thin-skinned parts are light- 

 greyish, the solid parts dark ; Avhen a figure has been drawn in 

 this way, the fact is specially mentioned below. The other 

 figures (the diagrams excepted) have been shaded in accordance 

 with the shape of the parts : the membranous parts are light 

 greyish, while on the fii'm chitin dark shading is opposed to 

 white. 



Fig. 1.— Head of Glossina niorsitans, Westw., i, x 11 : I, basal inflated 

 part of the labium ; j^, palpus. 



Fig. 2. — External mouth-parts and pharynx of Glossina morsitans, 

 Westw., 6 , seen from the side, x rather less than 21 : a, labrum ; b, hypo- 

 pharynx ; c, labium ; d, its first segment ; e, its second segment ; /, 

 labellum ; g, basal part of the left maxillary palpus ; li., anterior wall of 

 the membranous cone ; i, left apodeme of the labrum : k, posterior wall 

 of the membranous cone ; I, pharynx ; m, its upper process ; n, solid part 



* According to M. Edouard Foa [135], when the Tsetse bites the 

 proboscis "disappears completely in the llcsh," while Lieut. -Col. Bruce 

 writes (vide Chapter VII., Appendix A, p. 274):— "The act of feeding is 

 remarkably quick. From the moment of settling on the animal until 

 the fly is fully blown out with blood is often as little as 20 to 30 seconds." 

 — E. E. A. 



