Structure of the Crystalline Lenses of Animals. 201 
that in the lenses of sheep and oxen there is only one series 
of luminous sectors, or one structure, corresponding with the 
intermediate set in the crystalline of fishes. This, however, 
is a mistake. By nicer means of observation I can distinctly 
see all the three structures in the lens of the sheep, the ox, 
and the horse; but, what is very singular, the nucleus and 
outer structure have positive double refraction, while the 
double refraction of the intermediate structure is negative ; 
a result exactly the reverse of that which I have obtained 
from the lenses of fishes*. If this triple structure is intended, 
as I have already conjectured, to correct aberration, or to im- 
prove vision, it will be a curious problem to determine how 
this is effected, and to connect the one structure with the ex- 
istence of a spheroidal lens without the aqueous humour, and 
the other with the coexistence of a flat lens and an aqueous 
humour. 
When the lens of a cod is prepared so as to indurate and 
retain its form and transparency, the process of induration 
confounds all the three structures in one; viz. a negative 
doubly refracting structure many times more intense than that 
which exists in the recent lens. When a lens thus indurated 
was exposed to polarized light, I observed round the axis of 
the lens a beautiful system of negative uniaxal rings, seven in 
number, and intersected with a well-defined black cross. 
When the polarized light passed through any equatorial dia- 
meter of the lens, a system of seven biaxal rings was beauti- 
fully displayed, the principal axis being of course negative. 
This system of rings was intersected by the black cross, 
when the plane of the equator coincided with that of primi- 
tive polarization, and they displayed the two dark hyperbolic 
branches when the inclination of these planes was 45°. These 
phenomena I observed most distinctly in the lens of the 
boneta; and I have seen them also in the lenses of the cod, 
the shark, and the flying-fish, which happened to have been 
preserved without any fissures or loss of transparency. 
In looking at a candle through the indurated lens of a cod, 
* Since this paper was printed in the Philosophical Transactions, I have 
been able to examine the lenses of the Sheep, the, Horse, and the Cow, 
at various ages, and to discover differences in the polarizing structure de- 
pending upon the age of the animal ; but, what is very strange, I have seen 
the polarizing structure change after death, and when one lens was placed 
in distilled water, and exhibited only two series of sectors,"both positive, 
I have observed the formation and development of two additional series 
of sectors, both negative, the one between the two positive series of sectors, 
and the other at the external margin, thus making four series, viz. 
+, —, +, —, commencing from the centre of the lens. 
Third Series. Vol. 8. No. 46. March 1836. Z 
