and of several other animals. 303 



himself could distinguish no object, and he admits that the eyes 

 of these birds do not shine in the dark. Besides sheep, cows, 

 horses, and several other animals which have the eyes shining, 

 would no doubt find themselves much embarrassed in absolute 

 darkness. If some quadrupeds, in fact, move with promptitude 

 and security in complete darkness, it is certainly not to their eyes 

 that they are indebted for it, but to some other sense. The 

 bats in which Spallanzani discovered this faculty, owe it, accord- 

 ing to him, to a sixth sense, of which we have no idea; and, accord- 

 ing to Cuvier,* to the extent of the membrane which their wing 

 presents to the air, and which renders it capable of feeling its 

 resistance, motion and temperature. 



It is true that the animals whose eyes shine in the dark are all 

 of the number of those whose motions the night rather favours 

 than impedes, when its shades are not too thick, and although 

 several others which feed, take their diversion, or provide for 

 their subsistence, during the night, have not the eyes shining, one 

 is yet tempted to search the cause of the agreement or con- 

 currence of these two circumstances, which we observe so fre- 

 quently to take place. 



The light does not act upon the retina by impulsion, as some 

 physiologists seem to think ; its action, although its nature is not 

 very well known, appears to be purely chemical ; and the sensi- 

 bility of the eye to the light, being on this account susceptible 

 of a sort of saturation, it was necessary, in order to let it have 

 all the delicacy which it would require to serve the animal in pro- 

 found darkness, either to take care that the eye should receive 

 but very little light during the day, or that this light, at least 

 what was superabundant, should be immediately sent off by some 

 reflector, which would not allow it to enter into combination. If, 

 on the contrary, it were useful for the cat, that its eye should be 

 filled with light in the night-time, nature would take care to pre- 

 vent it from entering the light during the day, or provide that 

 the little which its Ruyischian membrane might receive through a 

 contracted pupil, should be instantly thrown out. 



To conclude, the preceding observations seem to me sufficient- 

 ly to prove, 1st, That the shining of the eyes of the cat and of 

 other animals, which present the same phenomenon, does not 

 arise from a phosphoric light, but only from a reflected light ; 



