BREEZE-FLIES. 31 



satisfactory information. Its colour when young is white, 

 but as it advances towards maturity it becomes browner, 

 and finally of a deep dark brown approaching to black : 

 having attained its full size it presses itself against the 

 upper part of the tumour, and by some unknown process 

 makes an aperture in the hide of about sufficient size to 

 admit a pea ; through this the larva wriggles itself a seg- 

 ment at a time until it comes quite out, and falling to the 

 ground seeks a convenient retreat in which to become a 

 chrysalis. 



The chrysalis is of a dark brown colour, and in figure 

 somewhat resembles the half of a walnut-shell, being 

 narrower at one end than the other, flat on one side, and 

 very rounded and convex on the other : after lying on the 

 ground for some weeks a portion of the indurated skin or 

 cover, of a triangular shape, is forced up at the smaller end, 

 and through the aperture thus occasioned the fly emerges. 



The fly is large and handsomely coloured ; although the 

 presence of the larva in the backs of cattle is frequently 

 observable, the insect in its perfect state is rarely met with, 

 and very few of our cabinets possess good specimens : it 

 flies with rapidity, but apparently without noise, and never 

 ventures over water. 



The act of oviposition appears to be attended with se- 

 vere suffering, or apprehension at least, which makes the 

 cattle run wild and furious, and gad or stray from the 

 pastures, and hence the ancient epithet of gad-fly. When 

 oxen are yoked to the plough, the attack of this fly is 

 attended with real danger, since they become perfectly un- 

 controllable, and often run directly forwards through the 

 hedges, or whatever obstructs their way. On this account 

 many ploughs are provided with a contrivance for setting 

 the oxen immediately at liberty. When the cattle are at- 

 tacked by this fly it is easily known by the extreme terror 



