CH. XI.] THE GAD-FLY. 207 



to the mountains covered with snow and ice ; with 

 so much horror do they avoid so minute an insect 

 hovering in the air. This fly endeavours to lodge 

 its egg on the back of the deer, which being- effected 

 the worm perforates the skin, remains under it the 

 whole winter, and in the following- year becomes a 

 fly." 



Although Linnaeus has attributed the perforation 

 of the skin to the larva, it is probable that the same 

 process which has already been detailed in treating 

 of the oestrus bovis, is also followed by this species. 

 But another kind of oestrus lodges near the gullet 

 of the deer, and there the larvae take up their abode 

 in families consisting of one hundred or more indi- 

 viduals. At each side of the root of the tongue 

 there is, according to Reaumur, a slit, in the pharynx 

 or gullet of the deer, which leads to two fleshy ca- 

 vities, which he calls purses. We do not know, 

 says he, of what use they are to these large animals, 

 but they are essential to the worms which are deve- 

 loped within them. If they are not made for these, 

 if they are useful to the deer, at all events, He who 

 constructed the cavities, and formed the insects, 

 knew that they were necessary to the existence of 

 these worms, and so taught them to lodge in their 

 destined repositories ; for all that is essential to their 

 nourishment and growth is contained within these, 

 and is not to be found elsewhere. The question is 

 how the perfect insect contrives to deposite its young 

 in a spot which none but an anatomist can detect, 

 and to reach which requires the boldness and dex- 

 terity of a creature which is regardless of its own 

 life. If we consider that nature has endowed the 

 deer with the power of ejecting any substance an- 

 noying the nostrils, by sneezing — the power of en- 

 veloping any thing irritating the palate in a viscid 

 saliva, or crushing it by means of grinder teeth, we 

 must give due credit to a fly, which, in spite of these 

 obstacles, manages to reach the cavities in question. 



