Mr. Clark'/ Obfervations on the Genus Gtjirus, 295 



pillar, the wound in the ikin is moftly clofed up, and healed within 

 a few days. 



The chryfalides continued in that ft ate from about the latter end 

 of June until about the middle of Auguft, when the fly appeared. 

 I have, notwithstanding, obferved full-grown larva- in the backs of 

 the cows as late as September, which muft have produced their 

 flies as late as November or December, or, perhaps, in the enfuing 

 fpring. 



This larva, in making its exit, is expofed to imminent danger, if 

 on land, of being trod on by the cattle, or picked up by birds. If 

 in the water, where the cattle ftand during great part of the day at 

 this feafon of the year, it periihes, or becomes the food of fillies. 



The perfect infect, on leaving the chrjfa/is, forces open a very 

 remarkable, margin ated, triangular lid, or operculum (fee fig. 4), 

 which may be traced in the Ikin of the larva y and is fituatcd on one 

 fide of the fmall end. 



The Oeftrus Bovis, in its perfect ftate (fig. 5 and 6), is the largefb 

 of the European fpecies of this genus, and is very beautiful. For 

 its defcription fee the conclufion of this paper. 



Although its effects on the cattle have been fo often remarked, yet 

 the fly itfelf is rarely feen or taken, as the attempt would be 

 attended with confiderable danger. The pain it inflicts in depo- 

 fiting its egg is much more fevere than in any of the other fpecies. 

 When one of the cattle is attacked by this fly, it is eafily known by 

 the extreme terror and agitation of the wliQle herd : the unfortunate 

 object of the attack runs bellowing from among them to fome dis- 

 tant part of the heath, or the nearer! water, while the tail, from 

 the feverity of the pain, is held with a tremulous motion ftraight 

 from the body, in the direction of the fpine, and the head and 

 neck are alfo ftretched out to the utmoft. The reft, from fear, 



generally 



