3 
or curve of the lens took place, and also by consideration of the static condition 
of the circulation in the gland, which was intimately connected with the dynamic 
action of the heart and arteries, and with the varying pressure exercised on the 
surface of the fishes' body at different depths under the surface of the water. The 
meaning of this peculiar arrangement of vessels on the choroid gland was thus 
interpreted, in connection with the rislc of injury to which the minute structures 
within the sclerotic capsule might be exposed, by great variation of pressure or 
tension of blood in the circulatory system itself, and by the influence of external 
pressure of water on the cornea of the fishes' eye, which formed a part of the 
tegumentary covering of the fish. 
The following general conclusions were arrived at in a brief summary of 
the anatomical and physiological points discussed : — 
1. That the fishes' vision is perfect for near objects, and that the great 
refractive power of the lens (a prolate spheroid having great density of 
substance) is adequate to the production of a detined picture at short 
focal distance, even when rays of light pass through so dense a medium as 
water; objects in the air near the water being seen also just as if they 
touched its surface at the point where the ray is bent. 
2. That no " accommodation" such as is known to exist in the human eye 
for the perfect definition of objects at a distance occurs in fishes — or at 
least is not provided for in the same manner ; the passive state of the 
fishes' eye being that in which it is enabled to see near objects, no active 
or physiological change appears necessary for ordinary vision, whilst 
physical dispersion of light on the water renders distant objects less liable 
to excite attention. 
3. That the iris has no power of reflex action on stimulus of light, and 
its immobility is in harmony with the optical deficiency of * accommodation' 
and the physically deficient illumination of the waters. 
4. That the choroid gland is not an organ intended to assist or produce 
" accommodation " of focal distance of the lens, but that its vascular 
character, and the absence of any muscular or gland element in its com- 
position, lead necessarily to an interpretation of functions directly relating 
to the static condition of the circulation fluid, and the changes of 
dynamic force exerted by the heart under varying pressure from without 
on the fishes' body. That, in fine, by such an arrangement (analogous 
examples of peculiarities in the venous circulation of Mammals and other 
animals dwelling in the water being well known), protection to the delicate 
tissues of the eye is afi^orded in the compensating balance of pressure 
within and without the circulating system. 
5. That there results from the globular shape of the eyeball, a secondary 
reflection of rays of light from the bottom of the eye against the inner 
pigmented surface of the choroid, which may perhaps mtensily the retmal 
