STRUCTURE OF THE CRYSTALLINE LENSES OF ANIMALS. 
39 
13. Tench. — This fish has a very small eye, and a small lens. Owing to the faint- 
ness of the polarized tint I have observed only one series of luminous sectors, whose 
character is positive. 
14. Perch. — The lens of this fish, like that of the tench, exhibits only one set of 
luminous sectors by polarized light, and their character is also positive. 
15. Gudgeon. — The teeth of the fibres are very distinct. I have observed only one 
series of luminous sectors, which are positive. 
16. Cat-fish. — This is a poisonous fish from Georgia. The teeth of the fibres are 
very fine. 
17. Bed Trout. — Its lens was nearly spherical, and 0*244 of an inch in diameter. 
It distinctly depolarized three series of luminous sectors, the inner and outer ones 
being negative, and the intermediate one positive. The teeth of the fibres are very 
distinct. 
18. Hickory Chad. — This fish is from Georgia. The fibres are distinctly seen. 
19. Cavala. — This fish is from Georgia. On one side of the lens there are two 
short septa. The secondary colours produced by the teeth of the fibres are very 
distinct. 
20. Stingarie. — This is a poisonous fish from Georgia. The lens is of an oblong- 
form when viewed in the direction of the axis of vision. The two septa on one side 
are very long. 
21. Skip-jack. — The teeth of the fibres are short, like those of quadrupeds. 
22. Black-fish from Georgia. — The fibres of its lens are large, and the colours 
which they produce very finely seen near the septa. 
23. Sheep-head from Georgia. — The fibres of its lens are unusually large*. 
24. Fish from Singapore. — Mr. George Swinton sent me a number of the eyes of 
this fish, but the name has been lost. Its lens has the form of an oblate spheroid, 
the axis of which is the axis of vision. This axis is 0*60 of an inch, and the equa- 
torial diameter 0*70. The secondary colours produced by the teeth are finely dis- 
played. 
§ 3. On the Anatomical and Optical Structure of the Crystalline Lenses of Animals, 
particularly those of the Lion, Tiger, Horse, Ox, and other Quadrupeds. 
In the two preceding sections I have described the two simplest combinations of 
fibres which characterize the structure of the crystalline lens in animals. The lenses 
of birds possess the first or simplest structure ; the lenses of fishes in general exhibit 
either the first or the second structure ; and we shall now show that the lenses of the 
Mammalia in general, with the exception of the liare and the rabbit, and other qua- 
drupeds of peculiar habits, are characterized by a third and a more complex struc- 
ture, in which three septa diverge from each pole of the lens at angles of 120°, the 
* See Philosophical Transactions, 1833, p. 329. 
