HARDWICKE'S SCIENCE-GOSSIP. 



105 



muscles seem to serve also for raising and lowering 

 the rest of the mouth, for there are no others to 

 do it. 



In the thorax are two salivary glands that termi- 

 nate in a pair of ducts. The pair join, and form the 

 salivary duct shown at sd, fig. 53. This has a valve 

 at v to control the emission of saliva, and it ter- 

 minates in the lingua or tongue, /. In biting-flies it 



membrane (see figure). Joined to these processes 

 is a pair of longitudinal muscles arising from the 

 base of the mentum. The contraction of these 

 would naturally draw the processes together, and so 

 shut the lobes of the labium, while the contraction 

 of the transverse muscles k would perhaps tend to 

 separate them. 

 To the under side of the floor of the mouth, at e, 



Fig. 54. Mouth of Tetanocera; diagram illustrating the 

 action of the pharynx, x 45 diam. ; ph, Pharynx ; c, Its tip, 

 where numerous muscles are attached; Ibr, Commencement 

 of labrum: a, Great pharyngeal muscle; o, small muscle; 

 as, (Esophagus j r, Eoof of the mouth, which moves up and 

 down. 



Fig. 55. Head of Tetanocerus marginuta, x 14 diam. 



Fig. 56. Head of Sepedon sphegeus, x 14 diam. 



is the injection of saliva into the wound made by 

 the labrum that produces irritation and swelling. 



The whole of the second and third joints of the 

 mouth are called the labium. This is of three parts 

 — an outer plate (mt, Gg. 53), which is the mentum ; 

 an inner plate, e, which forms the floor of the 

 mouth, and is the labium proper; and, thirdly, a 

 pair of lobes. 



The mentum terminates in a pair of long processes 

 (/",fig. 53), which are attached to the outer skin of 

 the lobes by means of a triangular thickening of the 



Fig. 57. Head of Loxocera ichneumonea, 12 diam. 



is attached a muscle arising from the tip of the 

 pharynx, which bends down the labium when the 

 fly wishes to bring its lancets into action. 



The inner surfaces of the lobes are traversed by 

 about thirty minute gutters, generally known as 

 " false tracheae," but which, since that name would 

 lead one to suppose that they are closed tubes 

 instead of open gutters, we prefer to call " capillary 

 channels." The food of the fly, which is almost 

 entirely liquid, is collected by these, and passes 

 between the labrum and labium into the pharynx, 

 which, as before noted, supplies the power of suc- 

 tion. 



The whole mouth is liberally supplied with 

 tracheae, which ramify so much that even each of 

 the hairs on the exterior surfaces of the lobes has a 

 separate branch. 



We hope that this figure and description will 

 enable amateur entomologists to understand how a 

 fly eats, which is somewhat difficult to make out 

 from specimens prepared in the ordinary way. 



Eig. 56 is an outline of the head of Sepedon sphe- 

 geus, a fly belonging to the same sub-family as 

 Tetanocera, and in many respects resembling that 

 genus. It is not common enough to be described 

 here, but the drawing is given to show how widely 

 the antennae differ from the ordinary type prevailing 

 among the Muscidse, and approach the type found 

 in the Conopidae. 



Passing over several sub-families, we come to the 

 Psilides (i.e. " smooth flies "), to which belong two 

 iusects better known than liked; viz. the Cheese-fly 

 (Piophila casei), and the Eacon-fly (P. luteata). 

 These are the parents of the " hoppers " which 

 infest cheese and bacon. 



Belonging to this sub-family there is a fly of very 

 paradoxical appearance, named Loxocera ichneu- 

 monea. The name Loxocera (meaning "oblique 

 horn ") is given to the genus because the antennae, 



