Microscopical Essays. 



275 



animal that they infer!:, we find another fpecies of infects feeking 

 their food in the more vital parts, and feeding on the flefh of the 

 animal, while full of life and health. M. de Reaumur has given 

 an h if lory of a fly (oeftrus bovis) which lives upon the backs, and 

 feeds on the flefh of young oxen and cows, where it produces a 

 kind of tumor. The fly lodges it's eggs in the flefh, by making a 

 number of little wounds, in each of which it depofits eggs, fo that 

 every wound becomes a nefl, the eggs of which are hatched by 

 the heat of the animal. Here the larva finds abundant food at 

 the fame time that it is protected from the changes of the wea- 

 ther ; and here they flay till they are fit for transformation. The 

 parts they inhabit are often eafy to be discovered by a kind of 

 lump, or tumor, which they form by their ravages ; this tumor 

 fuppurates, and is filled with matter ; on this difgu fling fubfiance 

 the larva feeds, and his head is always found plunged in it. 

 When the time of their metamorphofis is ready, the larva falls 

 upon the ground, and feeks a convenient place for the operations 

 of the enfuing change. 



There is a fpecies (oeftrus hemorrhoidal is) which depofit their 

 eggs in the rectum of horfes, it being in the interlines of thefe 

 only that they can be nourifhed. M. Vallifinieri has . given an 

 account of the introduction, of thefe eggs into the horfe, as ob- 

 ferved by a friend of his who was looking- at fome that were 

 feeding quietly in a meadow : on a fudden they began to leap and 

 jump, roll themfelves on the ground, then run, beat about their 

 tails, and were otherwife violently agitated ; perfuacled that thefe 

 extraordinary motions were produced by a fly that was buzzing 

 about them, he obferved them narrowly. The fly not being able 

 to fueceed in it's attacks on thefe, quitted them, and flew towards 



L 1 2 a mare. 



