ISO ORIGIN OF SPECIES 



than the mole; and I was assured by a Spaniard, who had 

 often caught them, that they were frequently blind. One 

 which I kept alive was certainly in this condition, the cause, 

 as appeared on dissection, having been inflammation of the 

 nictitating membrane. As frequent inflammations of the eyes 

 must be injurious to any animal, and as eyes are certainly 

 not necessary to animals having subterranean habits, a re- 

 duction in their size, with the adhesion of the eyelids and 

 growth of fur over them, might in such case be an advan- 

 tage; and if so, natural selection would aid the effects of 

 disuse. 



It is well known that several animals, belonging to the 

 most different classes, which inhabit the caves of Carniola 

 and of Kentucky, are blind. In some of the crabs the foot- 

 stalk for the eye remains, though the eye is gone; — the 

 stand for the telescope is there, though the telescope with 

 its glasses has been lost. As it is difficult to imagine that 

 eyes, though useless, could be in any way injurious to ani- 

 mals living in darkness, their loss may be attributed to dis- 

 use. In one of the blind animals, namely, the cave-rat 

 (Neotoma), two of which were captured by Professor Silli- 

 raan at above half a mile distance from the mouth of the 

 cave, and therefore not in the profoundest depths, the eyes 

 were lustrous and of large size ; and these animals, as I am 

 informed by Professor Silliman, after having been exposed 

 for about a month to a graduated light, acquired a dim per- 

 ception of objects. 



It is difficult to imagine conditions of life more similar 

 than deep limestone caverns under a nearly similar climate; 

 so that, in accordance with the old view of the blind ani- 

 mals having been separately created for the American and 

 European caverns, very close similarity in their organisation 

 and affinities might have been expected. This is certainly 

 not the case if we look at the two whole faunas; and with 

 respect to the insects alone, Schiodte has remarked, "We are 

 accordingly prevented from considering the entire phenome- 

 non in any other light than something purely local, and the 

 similarity which is exhibited in a few forms between the 

 Mammoth cave (in Kentucky) and the caves in Carniola, 

 otherwise than as a very plain expression of that analogy 



