300 M. Prevost on the shining of the Eyes of the Cat, 



Dessaigne"*s experiments, that neither the fluids nor the sub- 

 stances which have imbibed them manifest this property. 



Besides, as I have already insinuated, the eyes of the cat do 

 not shine either in absolute darkness, or even in a very intense 

 although imperfect darkness. A certain degree of light is al- 

 ways requisite, which may indeed be very feeble, but still quite 

 perceptible. I have kept myself several times, thirty or forty 

 minutes together, in dark places with cats, which mewed to each 

 other, or devoured their prey in their usual grumbling manner, 

 yet without their eyes manifesting any luminousness. I have 

 caressed, provoked, tickled, pinched and frightened in the dark 

 a very good natured cat, which has bitten and scratched me in 

 frolic or in anger, but without its eyes having ever shone. Yet 

 some instant before or after, the eyes of all these cats shone as 

 usual, when they were suitably exposed to a certain degree of 

 light. But what convinced me fully that the eyes which shine 

 in the dark, owe this property only to the faculty of reflecting 

 the light more strongly, is, that the eyes of all the animals that 

 are susceptible of presenting this phenomenon, are evidently, 

 and as appears to me exclusively, organized for this purpose. 



It is known that *' the inner layer of the choroid coat, which 

 appears to be of a firmer texture than the rest of its thickness, 

 and which bears the name of Ruyischian membrane, is lined in 

 man and in several other animals, with a blackish, or even abso- 

 lutely black and dull mucosity, which may be detached or wiped 

 off* with the finger or a pencil, and which serves to prevent the 

 rays reflected by the internal walls of the eye from disturbing 

 the vision. Now, the bottom of the Ruyischian membrane is 

 only covered with a layer of that varnish through which 

 its colour, which varies in a singular degree according to 

 the species, is perceived. In man, and the monkey tribe, 

 it is brown or blackish ; in hares, rabbits, and hogs, of a 

 chocolate brown ; but the carnivora, the ruminantia, the pachy- 

 dermata, the solipeda, and the cetacea, have bright and shining 

 colours in this part. The ox has it of a beautiful gold green, 

 changing into sky blue ; the horse, the goat, the buffklo, the 

 deer, of a silvery blue, changing into violet ; the sheep of a 

 pale gold green, sometimes bluish ; the lion, the cat, the bear, 

 and the dolphin, have it of a pale gold yellow ; the dog, the wolf, 



