6o 



Insects and Disease 



regard to its structure, its methods of feeding and 

 its life-history. 



The large compound eyes are the most con- 

 spicuous part of the head (Fig. 39). In front, 

 between the eyes, are the three-jointed antennae, 

 the last joint bearing a short, feathery bristle. 

 From the under side of the head arises the long, 

 fleshy proboscis (Fig. 40). When this is fully 

 extended it is somewhat longer than the head; 

 when not distended and in use it is doubled back 

 in the cavity on the under side of the head. About 

 half-way between the base and the middle is a 

 pair of un jointed mouth-feelers (maxillary palpi). 

 At the tip are two membranous lobes (Fig. 41) 

 closely united along their middle line. These are 

 covered with many fine corrugated ridges, which 

 under the microscope look like fine spirals and 

 are known as pseudotracheae. Thus it will be seen 

 that the house-fly's mouth-parts are fitted for suck- 

 ing and not for biting. Its food must be in a 

 liquid or semi -liquid state before it can be sucked 

 through the tube leading from the lobes at the tip 

 up through the proboscis and on into the stomach. 

 If the fly wishes to feed on any substance such as 

 sugar, that is not liquid, it first pours out some 

 saliva on it and then begins to rasp it with the 

 rough terminal lobes of the proboscis, thus re- 



