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DIPTERA. 359 
under the ground, and, finally, after having existed in these 
two elements, enjoy, high in the air, the pleasures of flight ' 
The third group of Brachycera is that of the Dicheta ; that is, 
those flies having two-fibred suckers. Among these are classed 
the Cstri, the Conopes, and the flies properly so called. 
The genus Cistrus, the Gad, Bot-fly, or Breeze, comprises those 
formidable insects which attack the horse, the sheep, and the ox.* 
The labours of Réaumur, in his admirable Memoirs, and those of 
M. Joly, Professor of Zoology to the Faculté des Sciences de 
Toulouse, who published some most valuable researches on this 
subject, in 1846, will guide us in the following brief explanation. 
The following is the description given by M. Joly of the Gad- 

Fie’. 41.—Horse-fly, male (Aistrus (gasterophilus) Fig. 42.—Horse-fly, female (Gistrus (gasterophiius) 
equ’). equi). 
fly (Gistrus equi), represented in Figs. 41, 42, which are taken 
from a drawing which accompanies that naturalist’s memoirs. 
The head of this insect is large and obtuse; the face light 
yellow, with whitish silky fur; the eyes blackish; the antennz 
ferruginous; the thorax grey; and the abdomen of a reddish 
yellow, with black spots. The wings are whitish, not diaphanous, 
with a golden tint, and divided by a winding band of blackish 
colour. ‘The feet are palish yellow. 
This species is found in France, in Italy, and also in the Kast, 
‘especially in Persia, and rarely in England. During the months 
of July and August, the Gstrus frequents pastures, and deposits 
its eggs chiefly on the shoulders and knees of horses. In order 
to do this, the female suspends herself in the air for some seconds 
over the place she has chosen, falls upon it, and with her abdo- 
5) 
* Mr. Bates, in his interesting “ Naturalist on the Amazons,” mentions an (istrws 
as occurring in those regions, which deposits its eggs in the human flesh, the larva 
causing a swelling which resembles a boil.—Ip. 
