Mr. Clark' j Obferva lions on the Genus Oeftrus* jn 



The teafing of other flies will fometimes occafion a motion of the 

 head fimilar to this ; but it ihould not be miftaken for it, as it is 

 never in any degree fo violent as during the attack of the Oeftrus. 



At other times this Oeftrus gets between the fore-legs of the horfe 

 whilft he is grazing, and thus makes its attack on the lower lip ; 

 the titillation occafions the horfe to ftamp violently with his fore- 

 foot againft the ground, and often ftrike with his foot as though 

 aiming a blow at the fly. They alfo fometimes hide themiclves in 

 the grafs ; and as the horfe ftoops to graze they dart on the mouth 

 or lips, and are always obferved to poife themiclves during a few 

 ieconds in the air, while the egg is preparing on the point of the 

 abdomen. 



When feveral of thefe flies are confined in a clofe place, they 

 have a particularly ftrong fufty fmell ; and I have obferved both 

 fheep and horfes, when teafed by them, to look into the grafs and 

 fmell to it very anxioufly ; and if they by thefe means difcover the 

 fly, they immediately turn afide and haften to a diftant part of the 

 field. 



The eggs of this fpecies appear of a darker colour than the for- 

 mer, and the circumftances attending their paiTage to the flomach 

 I am unacquainted with. 



The larva of the CE. hamorrholdalis) as well as the former fpecies, 

 appears to have been termed among the Romans, CoJJus*, which 

 feems to have been a general expreflion for any kind of foft imper- 

 fect animal, and to have been very analogous, and as extenfwely 

 applied as the word grub is at prefent in the Englilh language. 



The learned Charlton (Onomafikon Zolcon, p. 56), and afterwards 

 Dr\ Johnfon (fee Dictionary), have confidered afcarides as the fyno- 



* Vide Flavlus Vegetius Rtnatm dt JrU VtUrinaria y p. 6a, 64, 69, ed. Manh. 



nymou*- 



