Royal Society. 417 
one another at angles of 120°. The next degree of complexity is 
presented in the lens of the whale, the seal, and the bear, which 
contain, instead of three, four septa on each side, placed at right 
angles to each other in the form of across. In some specimens of 
lenses of whales and seals the author observed two septa from each 
pole, forming one continuous line, from each of the extremities of 
which proceeded two others, which were at right angles relatively to 
one another: so that there were in all five on each surface. The 
most complex structure is that of the lens of the elephant, which 
exhibits three primary septa diverging at equal angles from the pole, 
and at their extremities bifurcating into two additional septa, which 
are inclined to each other at angles of 60°, these latter being the 
real septa, to which the fibrous radiations are principally related. 
In some lenses of the elephant the author found the three septa 
immediately proceeding from the poles exceedingly short, and ap- 
proaching to evanescence ; so that he has no doubt that occasion- 
ally they may be found to have disappeared, and that the other six 
septa will then all diverge from the poles, like the radii of a hexagon, 
at angles of 60°. 
In all the preceding cases, where the arrangement of the fibres 
is symmetrical on the two sides, the septa on the opposite surface 
of the lens occupy positions which are reversed with respect to one 
another ; thus in the simple case of the double septa at each pole, 
the line formed by those of the posterior surface is situated at right 
angles to that formed by the septa of the anterior surface. Where 
there are three divergent septa at each pole, the direction of those 
on the one side bisect the angles formed by those on the other side ; 
and again, where the septa form a rectangular cross, those of one 
surface are inclined 45° to those of the other surface. 
It follows as a consequence of this configuration of the series of 
points which constitute the origins and terminations of the fibres, 
that all the fibres, with the exception only of those proceeding in a 
direct line from the extremities of any of the septa, must, in their 
passage from the one surface to the other, follow a course more or 
less contorted ; and must form lines of double curvature; that is, 
curves of which none of the portions lie in the same plane. 
The fibres of the lenses of quadrupeds gradually diminish in size 
from the equator or margin of the lens, where they are largest, to 
their terminations in the anterior or posterior septa. They are 
united together by small teeth like those of fishes; but, generally 
speaking, the teeth are smaller and less distinctly pronounced, and 
sometimes they are not seen without great difficulty. 
In the lens of the turtle, as well as in that of several fishes, the 
arrangement of the fibres, instead of being symmetrical on the two 
sides, as is the case in all the preceding instances, is different on the 
anterior and posterior surfaces; there being two septa on the for- 
mer, but none in the latter, which presents only a single polar point 
of convergence. 
The author has directed much of his attention to the optical pro- 
perties of these structures. Thelens of the salmon depolarizes three 
Third Series. Vol.8. No. 48. May 1836. 2U 
