2 ^ 
Mr. Home's Lecture 
As the change which the eye is to undergo is different, so 
are the parts which produce it. The cornea, in many fishes, 
is neither circular, prominent, nor elastic, and the ciliary pro- 
cesses are wanting. The straight muscles pass off in different 
directions, to prevent the eye from being pressed upon late- 
rally; the coats of the eye at that part are bony, in some fishes, 
to prevent the same effect ; and the bottom of the orbit, which 
in other animals is filled with fat and loose cellular mem- 
brane, has no such covering, but is a hard concave surface, to 
give resistance, and assist in flattening the eye. 
From the preceding observations, deduced from the struc- 
ture of the eye in different animals, it appears that there are 
two modes of adjusting the eye, one for seeing in air, the other 
for seeing in water ; and it is probably the want of this know- 
ledge that has misled former inquirers, by confining their re- 
searches to the discovery of some one principle common to the 
eyes of all animals. 
The crystalline lens, as the most conspicuous part, engrossed 
their whole attention, and they did not think any of the others 
capable of giving material assistance in producing so curious 
an effect. 
The ciliary processes, from their connection with the lens, 
were by some believed capable of bringing it forwards ; by 
others they were supposed to contract, and by that action elon- 
gate the eye, and remove the lens further from the retina : but 
these processes could never bring the lens forwards, unless the 
cornea was also moved forwards ; for the lens and processes 
forming a complete septum, the aqueous humour would pre- 
vent the lens from making any advance in that direction : 
and the processes themselves are neither strong enough in 
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