150 NUNNELEY, ON THE CRYSTALLINE LENS. 
This form is readily seen in the lens of almost any adult 
animal by the three sections into which it spontaneously 
separates. I think I have observed the septa to be always 
more regularly and distinctly marked on the posterior than 
on the anterior surface, probably on account of its greater 
convexity. 
4th. The fourth type is when there are four septa placed 
at right angles to one another, and being inclined at the two 
surfaces at angles of 45° to each other ; were the lens trans- 
parent and the septa seen at the same time, they would 
appear like the eight radii of an octagon, inclined 45° to one 
another. Few animals possess this arrangement ; the whale, 
seal, and bear being all that Brewster has found it in. 
Leeuwenhock described the whale has possessing five septa. 
In other lenses of the same animals there are two, or even 
three, centres of divergence, when there will be six radiations 
of fibres. 
In the human lens the arrangement of the fibres is the 
most complicated of any, for while the type is the mammalian 
tripod, and is best seen in the foetus, in the adult the planes 
are more numerous, In consequence of the primary planes 
immediately branching into secondary, so that a very com- 
plicated curvature of fibres exists; the septa upon the two 
surfaces frequently not being equal, those of the posterior 
being more numerous than those of the anterior. In the 
anterior nine septa and radiations are often found, in the 
posterior surface twelve, which Arnold regards as the more 
common arrangement in man. This complicity, however, is 
only in the more superficial layers, for towards the axis the 
normal mammalian triseptal division is preserved. 
The general arrangement of the fibres of the lens in dif- 
ferent creatures is most easily seen by immersing it for a few 
minutes in water at 180° F., then allowing it to dry in a 
warm room. In two or three days it will be found to have 
split into different sections, according to the direction of its 
septa, while the fibres then form good microscopic objects 
and are easily preserved by simple mounting in glycerine, 
but if kept im water they soon swell, the edges become very 
irregular, the substance granular, and then breaks up. 
Of the reason for these varying planes, or why they should 
differ so much in different animals, we are in complete 
ignorance ; no plausible conjecture has been offered. It has 
been suggested they are for the purpose of enabling the 
curves of the two surfaces of the lens to be modified so as to 
adjust the eye to vision at different distances. It for long 
has been a favorite idea with some anatomists and opticians, 
particularly with the latter, that this power of the eye to 
