Mr, Clark'j- Obfervat'tons on the Genus Oejlrus. 30J 



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

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

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

 on one horfe. 



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

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

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

 object. 



The Ikin of the horfe is always thrown into a tremulous motion 

 on the touch of this infedt, which merely arifes from the very great 

 irritability of the Ikin and cutaneous mufcles at this feafon of the 

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

 thefe mufcles a£l involuntarily on the flightefl: touch of any body 

 whatever. 



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

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

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

 hairs of the mane. But it is a fa6l worthy of attention, that the 

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

 fl:antly on thofe parts which are mofl: liable to be licked with the 

 tongue; and the ova therefore are always fcrupuloufly placed 

 within its reach. Whether this be an aft of reafon or of inftind, 

 it is certainly a very remarkable one. I Ihould fufpecl, with Dr. 

 Darwin *, it cannot be the latter, as that ought to direi5l the per- 

 formance of any ad in one way only. 



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

 the ftrongefl: examples of pure inftind, or of the mofh circuitous 

 reafoning any infcd is capable of. The eggs thus depofited 



* Zoonomia, Vid. Chapter on Inllind. 

 Vol. III. R r I at 



