PARASITES FREE DURING THEIR WHOLE LIFE. 



121 



cies which are here represented, and which differ as much 

 by their external characters as by their mode of Hfe. 



Another fly also attacks horses and cattle, and occa- 

 sionally even man, the Asilus crahroniformis, whose 

 wounds sometimes di'aw blood. Martins, the birds of 

 the twilight, which fly in flocks above the houses, 



^ e 



Fig. 11.— Ox-fly. 



Fig. 12.— Antenna of 0x-fl3\ 



describing circles and uttering shrill cries, are usually 

 infested by many vermin, among which we find a fly of 



Fig. 13.— Blue Fly. 



considerable size, which looks much like a spider, the 

 Ornithomya hirimdinis. It moves about among the 



