INDIRECT INJURIES CAUSED BY INSECTS. 151 



they then become perfectly unmanageable ; and, whe- 

 ther in harness or yoked to the plough, will run di- 

 rectly forward. At the season when the (Estrus infests 

 them, close attention should be paid, and their harness 

 so Constructed that they may easily be let loose. 



Reaumur has minutely described the ovipositor, or 

 singular organ by which these insects are enabled to 

 bore a round hole in the sliin of the animal and deposit 

 their eggs in the wound. The anus of the female is 

 furnished with a tube of a corneous substance, consist- 

 ing of four pieces, which, like the pieces of a telescope, 

 are retractile within each other. The last of these ter- 

 minates in five points, three of which are longer than the 

 others, and hooked : when united together tiiey form an 

 instrument very much like an auger or gimlet ; only, 

 having these points, it can bite with more effect^. He 

 thinks the infliction of the wound is not attended by 

 much pain, except where very sensible nerves are in- 

 jured, when the animal, appearing to be seized with a 

 kind of phrensy, begins to gambol, and run with such 

 swiftness that nothing can stop it. From this semblance 

 of temporary madness in oxen when pursued and bored 

 by the CEstrus, the Greeks applied the term to any sud- 

 den fit of fury or violent impulse in the human species, 

 calling such ebullitions an CEstrus. The female fly is 

 observed to be very expeditious in oviposition, not 

 more than a few seconds ; and while she is performing 

 the operation, the animal attempts to lash her oif, as it 

 does other flies, with its tail. The circular hole, made 



* Plate XVI. Fig. 3. Mr. Clark, however, is of opinion that the 

 QSstrus does not pierce the skin of the animal, but only glues its eggs to 

 it. Essay on the Bots of Horses and other Animals, p. 47. 



