74 MEDICAL ENTOMOLOGY 



itself; as will be seen from the figure, when the longitudinal rod at the 

 bottom of this system of levers is rotated upwards on the fixed point 

 at its anterior end, the wing is folded and the squama rotated in a 

 direction opposite to the base of the wing, while when it is rotated 

 downwards the squama is pushed in the opposite direction, that is, into 

 the same plane as the rest of the wing. 



Taking Tabanus as a type the composition of the thorax in the 

 Culicidae and the Muscidae, representing simpler and more complex 

 arrangements respectively, may be discussed briefly. 

 In the mosquitoes (Plate XIV, fig. 1), as one would 

 expect in creatures of less powerful flight, the sclerites are composed 

 of thinner and less rigid chitin. The thorax is less compact, longer 

 in proportion to its breadth, and more pointed in the middle line 

 ventrally, than that of Tabanus. The three pairs of legs are also attached 

 nearer together, and appear to arise, to use the words of Nuttall and 

 Shipley, from the apex of a pyramid. The disposition of the sclerites is 

 indicated in the figure. The prothorax is reduced, though not nearly 

 to so great an extent as in Tabanus, and consists of a large lateral 

 plate, the episternum, and a small sternum which can only be recognized 

 on dissection. The episterna are articulated to the cervical sclerites, 

 and there is in this form also a comparatively wide membraneous area 

 at the base of the neck, which can be seen to bulge when the mosquito 

 is feeding. The episterna occupy a considerable part of the wall of the 

 thorax, and extend as far as the first pair of legs. They bear near their 

 anterior borders the curious structures known as the patagia. These are 

 sausage -shaped bodies, distinctly elevated above the surface, and con- 

 nected internally with the prosterna by fibrous bands, in the same 

 manner as the epimera of the Tabanids are connected with the sterna 

 and sternella. The membraneous interval between the dorsal and lateral 

 walls of the thorax is triangular, and lies between the mesosternum 

 and the lateral plate of the prosternum. There is also a rather wide 

 interval between the mesothorax and the metathorax. 



One point which should be particularly noted in the anatomy of the 

 thorax of the mosquito is that there are two elevations posterior to 

 the scutum. The first of these is by common consent called the 

 scutellum, the second, which is hidden underneath the first when the 

 thorax is seen from above, is the post-scutellum, a part of the dorsal 

 wall of the mesothorax. This latter piece is referred to by Theobald as 

 the metanotum, but this is incorrect, for, as pointed out by Nuttall and 

 Shipley, there is a narrow slip posterior to this which is the true dorsal 



