77§ 



THE DiPTEkA 



IS composed oi a double cuticnlar wall carrying scales on its exterior, and 

 enclosing internally a cavity containing muscles, etc., among which the 

 filarial embryos can lie. There are, therefore, two tubes in the proboscis: 

 the first, large, lormed by the labrum-epi pharynx and the hypopharvnx, is 

 the blood-tube, up which the blood is sacked into the pharynx; while the 

 other, small, lying in the hypopharynx, is the saUvarv duct. Tiie first is 

 aflerent, the second efferent. 



Behind the eyes there is an area oi the head called the 'occiput,' which 

 carries different kinds of scales in different genera, as is seen by the following 

 diagram (Fig. 383). These scales may be differentiated into narrow curved, 

 scales, upright forked scales, and flat scales, the presence and character of 

 which have been made the means of classification. The upright forked and 



f g h i j k 



Fig. 383. — Various Forms of Scales found on Different Parts of a 



Mosquito. 



(After Theobald, from ' The Culicidae of the World.') 



a, Flat scale from abdomen; b, broad wing scale; c, another broad wing 

 scale; d, curved hair-like scale; e, narrow curved scale; /, fiat spindle-shaped 

 scale; small form of /; li and i, upright forked scales; j, twisted upright 

 scale; k, inflated scale. 



the curved scales occupy the middle area of the occiput, and alone are met 

 with in this species; but quite different arrangements are met with in other 

 genera. The extreme posterior area of the head is the nape. Below the eye 

 laterally is the area of the head called the ' gena.' At the back of the head is 

 the occipital foramen, through which the soft structures pass to the neck. 



Neck. — The neck is the soft connection of the head with the thorax. It is 

 strengthened with chitinous rods. 



Thorax. — The thorax shows the usual three divisions into pro-, meso-, and 

 meta-thorax, but of these the mesothorax is much the largest, and is often 

 called ' the thorax ' ; in fact, the pro- and meta-thorax are hard to see. It will 

 be remembered that a typical thoracic segment should show dorsally a notuin, 

 composed of pra;scutum, scutum, scutellum, and post-scutellumx ; ventrally 

 ■a, sternum, and laterally a pleuron, consisting of episternum and epimerum. 



