Air, Clark s Obfervatiom on the Genus Oefirus. 305 



poifing herfclf before the part, depofits it in the fame way. Ti. e 

 liquor dries, and the egg becomes firmly glued to the hair: this 

 is repeated by various flies till 4 or 500 eggs are fometimes plactd 

 on one horfe. 



The horfes, when they become ufed to this fly, and find it d 

 them no injury, as the Tabani and Conopes, by fucking their blood, 

 hardly regard it, and do not appear at all aware of its in Odious 

 object. 



The (kin of the horfe is always thrown into a tremulous motion 

 on the touch of this infect, which merely arifes from the very e;reut 

 irritability of the lkin and cutaneous mulcles at this feafon of the 

 year, occafioned by the continual teafing of the flies, till at length 

 thefe mufcles act involuntarily on the flighted touch of any body 

 whatever. 



The infide of the knee is the part on which thefe flies are mod 

 fond of depofiting their eggs, and next to this on the fide and back 

 part of the lhoulder, and lefs frequently on the extreme ends of the 

 hairs of the mane. But it is a fact worthy of attention, that the 

 fly does not place them promifcuoufly about the body, but con- 

 stantly on thofe parts which are mod liable to be licked with the 

 tongue; and the ova therefore are always fcrupuloufly placed 

 within its reach. Whether this be an act of rcafon or of inftinct, 

 it is certainly a very remarkable one. I fhould fufpect, with Dr. 

 Darwin *, it cannot be the latter, as that ought to direct the per- 

 formance of any act in one way only. 



Whichever of thefe it may be, it is, without doubt, one of 

 the ftrongeft examples of pure inftinct, or of the molt circuitous 

 reafoning any infect is capable of. The eggs thus depofited 



* Zoonomia. Vtd. Chapter on Inftinct. 



Vol. III. Rr I at 



