OF NATURAL HISTORY. 105 



trary to tke general oeconomy of Nature, that no reafon- 

 iiig or theory can account for a fa6l fo uncommon, till far- 

 ther difcoveries fhall be made in the hlflory of thefe fur- 

 prlfing animals. What is ftill more fmgular, after the cater- 

 pillars are transformed into the chryfalis ftate, the neuters 

 are inceiTantly and anxioufly employed in preferving the 

 chryfales from humidity when the weather is wet, and in ex- 

 pofing them to the warmth of the fun when it is fair. Thefp 

 chryfales are larger than the animals themfelves, and yet they 

 carry them off with eafe and rapidity. 



The fixth order of infe6ls is termed diptcra^ or two-wing- 

 ed infects. The different fpecies of this order, befide v/ings, 

 are furnifhed with what is called a Ijalter or a po'ifcv^ which 

 is lituated under each wing, and is terminated by a ccpltu- 

 luniy or knob. This order comprehends ten genera and a mulr 

 titude of fpecies. The caterpillars of the oejlrus^ or gadjly, 

 lie concealed in the fkins of cattle, where they are nourifh- 

 ed during the whole winter. The perfect infects are frequent 

 wherever horfes, cows, or fheep, are grazing. Sonie of 

 them depofit their eggs in the fliins of cows or oxen 5 others 

 depoiit them in the inteftines of horfes, to which they get 

 accefs by the anus ; and others in the noftrils of fheep. In 

 thefe habitations, the caterpillars reiide till they are fuU 

 grown, when they throw themfelves down to the earth, and 

 generally pafs the chryfalis flate under the firfl: ftone they 

 meet with. The mtifcay or common j^^ : The mouth of this 

 infedl conlifts of a foft, flefliy probofcis, with two lateral lips. 

 The caterpillars of fome of this genus devour the pucerons ; 

 others confume all kinds of putrid flefh -, others are found 

 in cheefe j others in the excrements of different animals ; 

 and many of them live in the water, and prefer that which 

 is moft corrupted and muddy. The mouth of the cidcx^ or 

 gnat confifts of a flexible flieath, inclofnig four briftles, or 

 pointed flings. The feelers of the female gnat are plain liks 



