126 



ZOOLOGY. 



the egg state, from five days to a week as a maggot, and 

 from five to seven days in the pupa state. It breeds 

 about stables. 



The Tachina-fiy is beneficial to man, from its parasitism 

 in the bodies of caterpillars and other injurious insects. 



The bot-fly (Fig. 160, Hypoderma 

 bovis) is closely allied to the house-fly, 

 but the maggot is much larger. The 

 larval bot-fly of the horse lives in the 

 stomach; that of the sheep in the 

 frontal sinus, a cavity in the forehead. 

 The Syrphus flies (Fig. 161, Syr- 

 phus politics) mimic wasps; their mag- 

 Fig. i6i.— syrphus poiitus gots are most useful in devouring 



aphides. 

 The fleas are wingless flies, allied to winged forms which 

 are intermediate between the house flies and crane-flies. 



In the two- winged gall-flies {Cecidomyia, etc., Fig. 162, 

 C. tritici, Hessian-fly) the body is small and slender, with 

 long antennae. The crane-flies (Tipula) are large flies, 

 standing near the head of the order, and, like the flea and 



Fi«. 162.— Hessian-fly. a, larva; b, pupa; c, incision in wheat-stalk for larva. 



gall-fly, the chrysalis is enclosed in a cocoon, there being 

 no pnparium or pupa-case, as in the lower flies. Lastly, 

 we have the mosquito (Figs. 163, 164), whose larva is 

 aquatic, and breathes by a process on the end of the body, 

 containing an air-tube. 



