NATURAL HISTORY. 



817 



larvae in horns and frontal sinuses of 

 Sheep, and remdrks that the mem- 

 branes lining these cavities were 

 hardly at all inflamed, while those 

 of the maxillary sinuses \yere hi;;hly 

 so. From this circumstance he is 

 led to suspect that they inhabit the 

 maxillary sinuses, and crawl, on the 

 di'ath of the animal, into these situa- 

 tions in the horns and frontal si- 

 nuses. When full-grown, they fall 

 through the nostrils, and change to 

 the pupa, or chrjsalis state, lying 

 on the ground, or adhering to some 

 blade of grass. The fly proceeds 

 from the chrysalis in the space of 

 about two months. 



" The manner," says Mr, Clark, 

 *' in which this species deposits its 

 " ova, has, I believe, not been do- 

 " scribed: nor is it easy to sea, 

 " though close to the animal at the 

 " time, exactly in what way this is 

 " accomplished, owing to the ex- 

 '* treme agitation of the sheep ; but 

 " the motions of the sheep after- 

 " wards, and the mode of de- 

 " fence it takes to avoid it, can 

 *' leave but little doubt that the 

 " egg is deposited on the inner mar- 

 " gin of the nostril. The moment 

 " the fly touches this part of the 

 *' sheep, they shake their heads, 

 .*' and strike the ground violently 

 " with their fore-feet ; at the same 

 " time holding t'leir noses close to 

 *' thecartii, they run away, looking 

 " about them on every side, to soe 

 "if the fly punsues: tht-y also 

 " smell to the graiis as they go, lest 

 " one should be lying in wait for 

 " them. If they obsiuve one, they 

 " gallop back, or take some other 

 *' direction. As they cannot, like 

 " (lie horses, take refuge in the 

 " water, they have recourse to a 

 *' rnt, or dry dusty road, or gravel- 

 *' pits, where they crowd together 



* Bruce's Travels, vol, T 

 Vol, XLVIl. 



" during the beat of the day, with, 

 " their noses held close to the 

 " ground, which renders it difficult 

 "for the fly conveniently to get at 

 " the nostril. Observations odi 

 '• these flies are best made in warm 

 " weather, and during the heat of 

 " the daj', when, by driving the 

 " sheep from their retreats to the 

 ■•' grass, the attack of the fly, and 

 •' the emotions of the sheep, areea- 

 " sily observed." 



The other British oestri, are the 

 O. hccmorrhoidalis of Linnoaus, whose 

 larva, like that of the 0. equi re- 

 sides in the stomachs of horses, and 

 the 0. veterinus of INIr. Clark, the 

 larva of which is also found in simi- 

 lar situations. The O. hwmorrhoi- 

 dalii is about the size of a common 

 window fly, with pale dusky wings, 

 brown thorax, abdomen white at the 

 base, black in the middle, and red 

 at the tip. The O. •veterinus is 

 nearly of similar size with theO. equi^ 

 and is entirely of a ferruginous co- 

 lour, with the abdomen more dusky 

 towards the tip. 



The exotic oestri are probably 

 numerous, but are at present very 

 little known. 



VV^hcther the formidable African 

 fly, described by Mr. Bruce, under 

 the name of ziinb *, or isaltsalj/a 

 may be referred to this genus or 

 not, 1 shall not pretend to deter- 

 mine ; there are, however, some 

 particulars in its history, which 

 would lead one to Suppose it an 

 oestrus. 



" This insect," says Mr. Brucc» 

 " is a proof how fallacious it is to 

 " judge by appearances. If we 

 " consider its small size, its weak- 

 " ness, want of variety or beauty, 

 " nothing in the creation is more 

 " contemptible and insignificant. 

 " Yet, passing from these to his hiS- 

 p. 388, and vol. V. p. 188. 



3 G tory, 



