Mr. ClArk'j Obfervations on the Genus Oejlrus. ^oy 



of the teeth and maftication to pafs through. On their arrival .at 

 the ftomach, they may pafs, mixed with the mafs of food, into the 

 inteftines ; and, when full grown, on dropping from the anus to the 

 ground, a dirty road or water may receive them. — If on the com- 

 mons, they are in danger of being crulhed to death, or of being pick- 

 ed up by the birds who fo conftantly for food attend the footfteps of 

 the cattle.' Such are the contingencies by which Nature has wifely 

 prevented the too great increafe of their numbers, and the total de- 

 flru(5lion of the animals they feed on. 



I have once feen the larva of this Oejlrus in the ftomach of an 

 afs : indeed there is little reafon to doubt their exiftence in the 

 ftomachs of all this tribe of animals. 



The perfect fly but ill fuftains the changes of weather ; and cold 

 and moifture, in any confiderable degree, would probably be fatal 

 to it. Thefe flies never purfue the horfe into the water. This aver- 

 fion I imagine arifes from the chilnefs of that element, which is 

 probably felt more exquifitely by them, from the high temperature 

 they had been expofed to during their larva flate. The heat of the 

 flomach of the horfe is much greater than that of the warmeft 

 climate, being about 102 degrees of Fahrenheit, and in their fly 

 flate they arc only expofed to 60, and from that to about 80 de- 

 grees. This change, if fuddenly applied, would, in all probability, 

 be fatal to them ; but they are prepared for it, by fuffbring its firfl: 

 efFecls in the quiefcent and lefs fenfible fl:ate of a chryfalis. I have 

 often feen this fly during the night-time, and in cold weather, fold 

 itfelf up, with the head and tail nearly in contadt, and lying appa- 

 rently in a torpid flate, though in the middle of fummer. 



It is worthy of remark, that the greater part of the ova depofitcd 

 by this fly, are taken up in confequence of the irritations of other 

 flies, as the Conopes^ Tabani, and Mufca^ who, 'by fettling on the flcin, 



R r 2 occafion 



