THE FLIES: DIPTERA 59 



balancers also act as organs of hearing. Two broad scales 

 are found on the sides of the thorax, just behind the wings. 

 The legs are fitted for running, and the pulvilli are large 

 and bear tubular hairs, which secrete a sticky fluid by means 

 of which the fly can walk on smooth surfaces, even when 

 upside down. 



The eggs, over one hundred in number, are laid usually 

 in horse-manure, and hatch within a day into smooth white, 

 almost transparent, conical, footless larvae, called maggots. 

 They have rudimentary mouth-parts, consisting only of a 

 few small hooks. The larvse feed for about a week, growing 

 rapidly and molting twice within that time, and then pass 

 into an inactive pupal stage within the larval skin. In a week 

 more the perfect insect appears by making a circular hole 

 in one end of the pupal case by means of a large bladder- 

 like bulb, which swells out on the forehead and is later with- 

 drawn into the head. The life-history is thus completed 

 within about two weeks, and as the imagoes soon lay eggs, 

 there may be several generations in the course of the summer. 

 On the approach of cold weather most of them die, though 

 some hibernate in sheltered places. 



The house-fly has always been considered a nuisance about 

 the house ; but lately a more serious charge has been laid at 

 its door, that of transporting on the pulvilli and proboscis 

 the germs of typhoid fever.. With the knowledge of its favorite 

 breeding-place it should be possible, by insisting on cleanli- 

 ness in stables, by the daily collection of manure and its dis- 

 posal in a closed place, or by treatment with chloride of lime, to 

 greatly mitigate, if not entirely destroy, this menace to health. 



Equally well known are the blow-fly (Calliph'ora vomito'ria) 

 and the bluebottle (Lucil'ia cae'sar), which deposit their eggs 

 on fresh and decaying meat. These flies hatch within a day, 

 and the larvas greedily devour the decaying material, not 

 hesitating, when that task is finished, to devour each other. 



