96 GNATS OR MOSQUITOES — CHAPTER VI 



connected by a delicate membrane, reflected on to them, 

 and thence to the floor of chitinous pharynx, the hypo- 

 pharynx, as already described, ends as a blind sac lying in 

 the root of the labium, just in front of the buccal cavity. 

 The anatomy of the latter is by no means simple, and so 

 far as I know, has hitherto remained unnoticed. 



As I have endeavoured to indicate in fig. F, plate IV., 

 the framework of the mouth springs from the strong 

 tergal plate running along the middle line of the head, 

 and from which springs the base of the labrum. From 

 this, on either side, runs down a strong lateral piece, which 

 shortly divides into two rods, enclosing an oval space, 

 the anterior of which appears to be really the basal piece of 

 the mandible. Reuniting below, these lateral pieces are 

 continued downwards to join with the strong but narrow 

 sternal plate that lies in the ventral middle line. This 

 sternal plate, however, is only single and median for a 

 short distance ; after which it divides into lateral rods, 

 united by a delicate membrane, which run back between 

 the lower borders of the eyes. Through this transparent 

 membrane, if we can successfully clear away the opaque 

 mass of structures lying above them, may be distinctly 

 traced the single median common duct of the salivary 

 glands, running forward to open into the fundus of 

 the hypopharynx. The pharynx, or intracephalic portion 

 of the digestive tube, is entirely chitinous and terminates 

 in a cup-shaped expansion, which forms the back of the 

 roughly spherical frame of the buccal cavity. This, as 

 already described, is in no way rigidly connected with either 

 the framework of the head, or the end of the hypopharynx, 

 continuity of the tubes being maintained only by a very 

 delicate membrane, and into the space between the two 

 structures a mass of mesoblastic tissue is pushed forwards, 

 especially below, and expands between the cupped end of 

 the pharynx and the delicate connecting membrane into a 

 thick mass composed mainly of peculiar spindle-shaped 

 cells. It is along with this mesoblastic intrusion that the 

 salivary duct and two large nerves are conducted to the 

 interior of the buccal bulb, and the presence and large size 



