130 



As to the other muscles of the eye, one only, an abductor, was 

 distmguishable from adjoining muscles. It is of large size compara- 

 tively, and it may be inferred powerful : by acting on it, seizmg 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 j^yth of an inch in diameter ; the iris dark 

 brown ; the pupil circular ; the lens about y^-grd 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," &c. 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 m 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 sjicculative 

 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. 



