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ber of veffels, in order to contribute to the increafe of fiich feather : 

 and who knows whetlier each of fuch fmall feathers may not have 

 been formed out of more than a thoufand vefTels ? And when we 

 reiie6l on the great number of feathers or hairs with wliicli the wing 

 of a fly or moth is covered, we fliall find it impoflible to conceive 

 the numbers of vcflels of which thefe infe6ls, though they appear 

 contemptible in our eyes, are compofed. Indeed, I am of opinion, 

 that many phyficians and furgeons cannot reckon up fo great a 

 number of veHels in a cat or a dog, as I imagine enter into the com- 

 pofition of a gnat. 



It was alfo at one time my opinion, that the ridges, or thicker 

 parts, in the wings of thefe flying infers, and which 1 have named 

 fmews, were only the boney parts of the wing to give it ftrength. 

 But when I perceived, that there were large blood-veflels in thofe 

 parts, I applied myfelf with all diligence to dilcover, if pofllble, 

 the current of blood in tiiofe vedels. 



For this purpofe, I took thofe butterflies which ]:)roceed from 

 the catterpillar that feeds on the afpin, the poplar, or the willow ; 

 and which, in fize and fhape, refemble the filk worm's butter- 

 fly. Their wings are, on both fides, covered with white feathers, 

 and, unlefs thefe are taken off, the membrane cannot be dif- 

 cerncd. Thei'e feathers I wiped from the wing witli a foft piece 

 of leather, as gently as poflible, to avoid injuring the wing or 

 hurting the butterfly. And I then applied the wing (while the 

 animal was alive) to the microfcope ; but, with all my attention, I 

 could not difcern the leaft current of blood in the veflels, thouah 

 if there had been any regular motion, I have no doubt but I fliould 

 have ieen it, and the rather, as this blocd was of a yellowiOi 

 colour; and, upon opening the large veffels in thefe wings, I have 

 often prefled out the blood which they contained. 



For tiie moft part, thefe large velTels lye in, or near, that boney 

 part of the wing which gives it ftrength; and I have often obferved 



