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As to the other muscles of the eye, one only, an abductor, was 
distinguishable from adjoining muscles. It is of large size compara- 
tively, and it may be inferred powerful: by acting on it, seizing it 
with a forceps, and drawing it upwards, the ball of the eye was re- 
tracted, thus denoting its office. I sought in vain for other muscles. 
That they were not discovered, supposing them to exist, is not sur- 
prising, considering the smallness of the organ and its peculiar un- 
insulated position, most unfavourable for discriminating the subordi- 
nate parts pertaining to it, such as the muscles. 
Relative to the constituent parts of the organs themselves, except- 
ing their delicacy and minuteness, I am not aware of any peculiarity. 
The eye-ball is about ;.th of an inch in diameter; the iris dark 
brown ; the pupil circular ; the lens about ;,rd of an inch in dia- 
meter. Traces of a vitreous humour, and also of an aqueous, were 
observable ; the former in the appearance of a cellular texture, as seen 
under the microscope with a high power; the latter as an exudation 
of moisture, a just perceptible quantity of fluid, when the ball was 
ruptured. From the situation of the eyes low down in the face, the 
optic nerves are necessarily of unusual length. 
The dissections, of which I have thus briefly given the results, I 
need hardly remark were made chiefly under water, and with the aid 
of the microscope. 
To return to the subject which led to the inquiry, viz. the subter- 
raneous eyeless Fauna brought to light by the Danish naturalist, you 
in your letter briefly advert to the speculations which this curious 
discovery gives rise to, as, ‘‘ whether these animals originally had 
eyes, and have lost them from want of use by inhabiting for ages 
dark caves; or, whether they were originally created without eyes, 
for those abodes where they have no occasion for them,” &e. Allow 
me to ask—fully appreciating the difficulty of solving such pro- 
blems—whether the preceding observations on the eyes of the Mole 
are not rather in favour of the latter than of the former solution? It 
is easy to imagine how the optic nerve and the more important parts 
of the organ of vision might diminish in size from little use ; but it 
is difficult to suppose that the same circumstance could have any 
material effect in obliterating a cavity in bone—the eye’s orbit—and, 
if the Mole’s eyes were thus originally designed, why may not the 
eyeless animals have been formed in the first instance without eyes ? 
Do not we see throughout Nature the most perfect harmony between 
the organic structure and the modes of life and habits of the living 
beings, so that the one is the true index of the other,—and that in 
the most minute details? Excuse my touching on these speculative 
questions, which, probably, from their nature, always must be specu- 
lative,—unless indeed the eyeless species are found otherwise identical 
with species possessing eyes, and there be found also a gradation in 
them, as to power and size in accordance with the degrees of light to 
which the individuals have been habituated, as in advancing from the 
open air and the entrance of the dark abodes to their deepest recesses. 
Also, excuse me if the matter of this letter should not be new to you. 
Lesketh How, Ambleside, April 28, 1851. 
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