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After remaining in the chryfalis (late about two months, 

 the fly appears. Sv:e the iltfcription at the conclufion, and 

 the H^urt.- r.f it ill the plate. 



" ft fiems hitherto to have been iiMiverfally bchevcd amonjj 

 raturahlls, that the female fly enters tlie anus of the h();fe, 

 in a very extrantdiiiary inaiintr, to dcpufite its egps. 

 Reaumur received the idea of ValHfnirri. and VaUifnieri of a 

 Dr. Gafpari, whofe obfcrvations 1 fliould fiifpeift originated 

 from feeing the hipi'obafca equina teazing the horfe, as is 

 very commonly ftcn ; and its ({ettiniir within the rei\um was 

 merely, it is probable, fiipplicd by his fancy and im.igina- 

 tio«. The objcdions to an idea of this fort are thcfe, ad- 

 mitting therewas any good foundation for fiich a fuppofition; 

 that the anus is rather clofcd tlian opened by any irritation 

 externally applied ; that the fly would be ciii(hed in at- 

 tempting to pafs the fpliintlcr of a horle's rcCtum ; and 

 having no means of holding, while depoliting its eggs, it 

 %vould be quickly forced out with the dung ; and it is 

 evident, that the whole of the ova, to the amount of fome 

 hundreds, mull all be dcpofitcd in one horfe, as it is 

 impoflibie if the fly fuivived, it could iinde'-go tliis punidi- 

 ment a fecond time ; for the heat and moilUirc of the reftum 

 would at lead dellroy its wings, and prevent its attaining a 

 fecond time this lituation. 



" I mention thcfc objeftions, not as they merely relate to 

 this fpccics, but that it may not be credited of the na- 

 falis, or indeed of any of them, that tliey really enter the 

 body ofthea'iimal, to obtain for their young a fituation there. 

 " I have not feen any writer who has conjectured the real 

 mode in which this fly depolites its ova ; which having dif- 

 covcred by repeated opportunities of witneffing it, 1 can fpeak 

 of with certainty. 



" The part chofen by this infeft for this pnrpofe is the lips 

 of the horfe, which is very dillrefTing to the animal from the 

 exceffivc titillation it occafions : for he immediately after its 

 touch rubs his mouth againll the ground, his lore legs, or 

 againfl a tree ; or if two are Handing together, liiey often 

 rub themfelves againll each other. 



" At the light of this fly the horfe appears much agitated, 

 and moves his head backwards and forwards in the air, to 

 baulk its touch, and prevent its darting on the lips ; but the 

 fly, watching for a favourable opportunity, depolits its 

 eggs from tlie point of the abdomen, and he . continues to 

 repeat his attacks on the lip, till the enraged animal en- 

 deavours to avoid it, by galloping away to a dillant part 

 of the lV:ld. If it then continues to follow, or teaze him, 

 his lail refource is in the water, where the oellrus is never 

 cbfervcd to purfue him. 



" The teazing of other flics may fometimes occafion a mo- 

 tion of the head fimilar to this ; but it (hould not be miilaken 

 for it, as it is never in any degree to violent as during the 

 attack of the oellrus. 



"At other times 1 havefeen this fly get between the legs of 

 the horfe whilil he is grazing, and then make his attack on 

 the lower lip. The titillation occafions the horfe to llamp 

 violently with his fore-foot againll the ground, and he often 

 ftrikei with his foot as though aiming a blow at the fly. They 

 alfo fometimes hide themfelves in the grafs ; and as the horfe 

 ttoops to graze, they dart on the moutli or lips, and are 

 always oblervcd to poize themfelves during a few feconds 

 in the air, vhilc the egg is preparing on the point of the 

 abdomen. 



" When fcveral of thefc flies are confined in a clofe place, 

 they have a particularly ftrong fully fmcU, fuch as we feel 

 when animals are confined in a clofe place : and I have 

 oblcrved both (hcep and horfes, when ttazed by them, to 

 look luCu the grafs, aud Imcll to it very anxiuuily ; and if 



B O T 



by thefe means they difcover the fly, they immediately turn 

 alide, and hallen to a dillant part of the Held. 



" The eggs of this fpecies .•■.ppear of a darker colour than 

 the former, a'ld are provided witlv a/i-to/ur, or foot-llalk from 

 the fmall end, the oppolite being obtufe, and provideif 

 with an operculum : it is alio ribbed in a tranfvcrfe diredion, 

 unlike the eggs of the preceding fpecies. 



" Our auocltors imagined that poverty or bad food engen- 

 dered thcfe anm^als, or that they were the oflipring of 

 putrefadlon. In Shakfpcare's Henry the Fourth, part ill, 

 the oilier at Roeheller fays, " peas and beans are as dank 

 here as a dog, and that is the ne.\t way to give poor jades 

 the bots ;" and the miferable nag of Petnichio is laid to be 

 fo " begnawn with the bots." When the animal is kept 

 from food, the bots are alfo ; and, it is natural to fuppoie» 

 arc then the moll troublefome : whence arofc the idea, that 

 {.overty or bad f )od could engender them. 



" Of the oellrus -velerinus. This infcft was known to 

 Linnxus, who gave it the name of nnJalU, from an idea of 

 its entering the iiollrils of the horfe, and depoliting its eggs 

 in the fauces : " Habitat in equorum fauce per naves 

 intrans." Linn. Syft. Nat. 2. p. liyx). which as it could not 

 well do without dellroying its own wings, is probably as 

 much a fable as the " mire per anum ininws," of the pre- 

 ceding fpecies. We have feen iowr chryful'nlds of this fly, which 

 were uniformly found under the dung of iiorics, which leads 

 to a fufpicion that they alfo inhabit the llomachof this animal. 

 The larva is at prcfent unknown ; but if it inhabited the 

 fauces of the horfe, it would produce fuch troublefome 

 fymptonis as could not cafily efcape the notice of thofe 

 whofe bulinefs it is to attend to the difeafes of cattle. Such 

 a difeafc has, however, never been dcfcribed ; nor after an e.s- 

 tcnlive opportunity, both in the dead and living fubjeft, have 

 I ever fcena hot in l\\e fauces of the horfe. Perhaps the bots of 

 the llomach, having crawled to the fauces in fearch of food, 

 after the death of the animal, might have given rife to this 

 idea : they may have even accidently bred tliere ; for there 

 is little room to doubt, that thcfe animals can live in any 

 part whatever of the alimentary canal, or the paffages 

 leading to it. For a figure of this fly, fee aifo the plate of 

 the ocjlri. 



" Of the oejlrus ovis. About the middle of June I pro- 

 cured fome luU grown larvae of the oe/Jrus ovis, from the in- 

 fide of the cavities of the bone, which fupports the horns of 

 the fheep. They are nearly as large as thofe of the large 

 horfe -hot, of a delicate white colour, flat on the under fide, 

 and convex on the upper, having no fpines at the divifions 

 of the fegments, though provided with two curved hooks 

 at the fmall end. The other extremity is truncated, with a 

 fmall prominent ring or margin, which feems to ferve the 

 fame purpofe, though in an inferior degree, as the lips of 

 the oe. equi and haemorrhoidales, by occafionally clofing 

 over, and cleaning the horny plate of refpiration. When 

 this margin opens, after clofing over the plates, a flight 

 fnap is fometimes heard, from the ftidden admiffion of 

 air. 



" When young, thofe larvx are perfedlly white and tranf- 

 parent ; except the two horny plates, which are black : aa 

 they increafe in iize, the fegments of the upper fide 

 become marked with two brown tranfvcrfe lines ; and fome 

 fpots are obfervable on the fides. 



" They move with conliderable qnickncfs, holding with the 

 tciitacula as a fixed point, and drawing up the body towards 

 them. On the underlide of the larmi is placed a broad line 

 of dots, which, on examination with ghill'es, appear to be 

 rough points, ferving, perhaps, the double purpofe of 

 affilling their paffage over tUe finooth aud lubricated fur. 



faces 



