| → wholly 1859 1860 1861 1866 1869 |
| may be attributed 1872 |
|
| → cave-rat, the eyes are of immense size; and 1859 1860 |
| cave-rat (Neotoma), two of which were captured by 1861 1866 1869 |
| cave rat (Neotoma), two of which were captured by 1872 |
|
| → thought that it regained, after living some days 1859 1860 |
| at above half a mile distance from the mouth of the cave, and therefore not 1861 1866 1869 1872 |
|
| → light, some slight power of vision. 1859 1860 |
| profoundest depths, the eyes were lustrous and of large size; but these animals, as I am informed by Professor Silliman, having been exposed for about a month to a graduated light, acquired a dim perception of objects when brought towards their eyes, and blinked. 1861 1866 |
| 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 perception of objects. 1869 1872 |
|
|
The eyes of moles and of some burrowing rodents are rudimentary in size, and in some cases are quite covered
by skin and fur. This state of the eyes is probably due to gradual reduction from disuse, but aided perhaps by natural selection. In South America, a burrowing rodent, the tuco-tuco, or Ctenomys, is even more subterranean in its habits than the mole; and I was assured by a Spaniard, who had often caught them, that they were frequently
which
kept alive was certainly in this condition, the cause, as appeared on dissection, having been inflammation of the nictitating membrane. As frequent inflammation of the eyes must be injurious to any animal, and as eyes are certainly not
to animals
subterranean habits, a reduction in their
with the adhesion of the eyelids and growth of fur over them, might in such case be an advantage; 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
and of Kentucky, are blind. In some of the crabs the foot-stalk for the eye remains, though the eye is
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 animals living in darkness,
their loss
→wholly
to disuse. In one of the blind animals, namely, the
→cave-rat, the eyes are of immense size; and
Professor Silliman
→thought that it regained, after living some days
in the
→light, some slight power of vision. In the same manner as in Madeira the wings of some of the insects have been enlarged, and the wings of others have been reduced by natural selection aided by use and disuse, so in the case of the cave-rat natural selection seems to have struggled with the loss of light and
|
