Mr. Clarkj Observations on the Genus Oeftrus. 30 



y*i 



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 

 interlines ; and, when full grown, on dropping from the amis to the 

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

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

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

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

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

 firuction of the animals they feed on. 



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

 afs : indeed there is little reafon to doubt their exiflence 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. TJiis aver- 

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

 probably felt more exquifitely by them, from the high temperature 

 they had beenexpofed to during their larva ftate. The heat of the 

 ftomach of the horfe is much greater than that of the warmed 

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

 ftate they are only expofed to 60, and from that to about So de- 

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

 be fatal to them ; but they are prepared for it, by fuffering its fir ft 

 effecls in the quiefcent and lefs fenfible date of & thry falls, I have 

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

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

 rently in a torpid ftate, 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, Tatam, and Mufc^ who, by fettling on the flrin, 



R 1 2 ocean" on 



