( 6Q ) 



particles like threads which prefented themfelves to my Ught, were 

 no other than optic nerves ; and that the larger and rounding ex- 

 tremity of each of thefe nerves was-deftined to occupy the fmall 

 cavity of each optical organ on the infide of the tunica cornea ; fo 

 that in a word, I may venture to pronounce, that every optical 

 organ feen in the tunica cornea is provided with its particular 

 optic nerve. 



As to the other extremities of the optic nerves, which, being litu- 

 ated towards the inner part of the head, are fmaller in fize : this 

 muft, I think, neceflarily be the cafe, partly becaufe the tunica 

 cornea dilates itfelf in a fpherical form, whence it neceflarily fol- 

 lows, that the optic nerves as they tend towards the internal part, 

 muft by degrees grow fmaller, and partly becaufe the place where 

 they terminate muft be fmaller than the fpace within the tunica 

 cornea. And who knows, whether that part in which the optic 

 nerves fo terminate, may not be the brain itfelf, not yet difcovered ? 



In order the better to fatisfy the curiofity of others on this fubject, 

 I placed fome of the optic nerves of this fly upon a glafs, before the 

 microfcope, which I delivered to the limner, in order that he might 

 make as accurate a drawing of them as he was able. 



Fig. 2, G H ftiews two of thefe optic nerves, the part H was placed 

 near to, or rather within the cavity of the optical organ ; the other 

 end G, towards the internal part of the fly's head. 



In fig. 3, at I K L are feven of thofe optic nerves, the larger ends 

 of which were alfo placed next the tunica cornea. 



Fig. 4, M N O P Q, fliews a great number of optic ner^'es 

 heaped together, the upper ends of which, as feen at the letters N O 

 P, were placed next the tunica cornea. When thefe nerves are 

 feen in fuch heaps as here pictured, their true length cannot be dil- 

 tinguiflied, but when lying together in a fmall number, and a mo- 

 derate fized parcel, the light may eafily be feen through them, 

 they being fomewhat tranfparent. All this is fliewn in the figure. 



I have in the courfe of my obfervations difcovered, that all the 



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