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ibme of thofe minute voracious maggots, (voracious 1 may juftly 

 call them, lince they prey upon a maggot not lefs than fifty times 

 their fize), which I judged were fo far grown, that without taking 

 any more food, they would foon be changed into flying animals. 



I had, at firft, no doubt that thefe aurelias or cryfales were of the 

 fame nature as thofe of common flics, namely, that when the maggot 

 is about to be changed into a cryfalis, its Ikin contracts, and by fuch 

 contraction becomes more firm and folid, and ferves the animal for 

 a fliell or cafe during the progrefs to its change, and then we call it 

 an aurelia or cryfalis, though it be not wrapped in fuch a web or 

 fpun cafe, as we obferve many other flying infed:s to be ; but upon 

 opening thefe cryfales or aurelias, I found the maggot within them 

 in its original fliape, although it had lain in the aurelia llate a fort- 

 night. And, upon viewing thefe things by the microfcope, I found 

 I had been miftaken in my former opinion, for the Ihell or cafe 

 which I have called a cryfalis^ was neither compofed of a web nor 

 of the flcin of the maggot itfelf, but I was obliged to conclude, that it 

 was formed by a concreted fubftance ifluing from the leaf of the tree, 

 for it had the appearance of fibrous or branched parts, from which 

 there ifliied fmaller ramifications. And I did not find a cryfalis in 

 any of the knobs I opened, excepting in thofe which I had kept in 

 glafl'es : one of thefe cryfales, as it lay in the knob, is fhewn at L. 



After fome weeks I obferved, that from thefe cryfales certain 

 blackifli flies were produced, which at their tails had fome oblong 

 parts formed in the nature of flings, and another fort of flies, rather 

 of a fmaller fize, but without any fuch appearance of flings. 



Fig. 9, reprefents one of thefe flies the fame fize it appeared to 

 the naked eye, and at the letters C D is ftiewn that part which had 

 the appearance of a fling, and was two thirds as long as the ani- 

 mal's body. But, upon placing this before the microfcope, it did not 

 at all appear like a fling, for it was covered with a great number 

 of fmall hairs, as ftiewn in Jig. 10 at the letters A B, and no aperture 

 was to be difcovered in it. Whereupon I began to confider that 



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