FLIES. 361 



which the two spiracles open. When these 

 anterior and posterior spiracles are present 

 there are no spiracles along the sides of the 

 body, as we saw in the caterpillar and grub. The 

 larva, after a series of moults, is ready to pupate; 

 it retires within its last larval skin, which shrinks 

 and hardens and becomes a seed-like puparium with- 

 in which the pupa is formed. (Plate 40, Fig. 3.) 

 When the adult emerges it pushes off the end of the 

 puparium, which is a little lid or cap, and makes 

 its way out of its prison. Adults may winter over 

 to be ready to lay eggs in the next spring. 



The Proboscis. — The house fly can neither bite 

 nor sting, for it does not possess the stylets, as the 

 majority of dipterous insects do. The mouth is 

 modified to form a fleshy proboscis, with muscular 

 expansions at the free end to form a kind of broad 

 sucking lip. (Plate 40, Fig. 4.) On the surface 

 of this lip are a series of parallel grooves, along 

 which the liquid food is drawn. But the house fly 

 is not only able to devour liquid food. We have 

 seen one standing on a sugar lump, and it seemed 

 to be playing with some of the grains with its 

 proboscis and front legs ; it was really preparing it. 

 The mouth of the fly is surrounded by 50 or 60 

 rods, or teeth, which are used for grinding hard 

 surfaces to reduce them to pow^der and so allow the 

 saliva from the fly's mouth to reduce them to 

 a sweet, sugary fluid which can be absorbed by 

 the fly. It is omnivorous, however, eating almost 

 anything which can be reduced to a liquid — sweet 

 or evil smelling and tasting. 



