Structure of the Crystalline Lenses of Animals. 197 
to allow the fibres to be packed without condensation into 
spherical laminz, their breadths must diminish as the cosine - 
of the distance from the equator. 
Although the prolate form of the spheroid indicates that 
the thickness of the laminz, or of their component fibres, 
must increase slightly towards the poles, yet I have not been 
able to prove this experimentaily, or even to determine the 
thickness of the fibres. I have more than once detached, by 
accident, a single fibre from the mass, and by an examination 
of the black line which forms its edges, I am satisfied that its 
thickness is at least five times less than its maximum breadth. 
Having thus determined the form and size of the fibres, we 
come now to a very delicate and interesting part of the inquiry, 
namely, to ascertain the mode in which the fibres are laterally 
united to each other, so as to resist separation, and form a 
continuous spherical surface. The remarkable mechanism by 
which this is effected was first pointed out to me by an optical 
phaenomenon. In looking ata bright light through a thin lamina 
of the lens of a cod, I observed two faint and broad prismatic 
images, situated in a line exactly perpendicular to that which 
joined the common coloured images. Their angular distance 
from the central image was nearly five times greater than that 
of the first ordinary prismatic images, and no doubt whatever 
could be entertained that they were owing to a number of 
minute lines perpendicular to the direction of the fibres, and 
whose distance did not exceed the x 5, or the 12,500dth 
1 
2500 
of an inch. 
Upon applying a good microscope to a well-prepared lami- 
na, I was delighted to observe the structure shown in fig. 2, 
where the two fibres, a 6, bc, are united by a series of teeth, 
exactly like those of rackwork, the projecting teeth of one fibre 
entering into the hollows between the teeth of the adjacent one. 
The length of the teeth, or 2p, is equal to about one half of 
mn, and this length of course diminishes towards the pole in 
the same ratio with the fibre. The breadth of the teeth is 
such, that five of them, namely, three of one fibre together 
with the two teeth of the adjacent fibre, which they inclose, 
are equal nearly to mn + np, which is the measure of the 
quantity B in the preceding formula. With an ordinary mi- 
croscope, the series of teeth between any two fibres seem to 
form a dark line, whose breadth is np; and it is in conse- 
quence of the interruption of the light thus occasioned, when 
the Jamina is dry, and the surfaces not in optical contact, that 
the fibrous lamina acts upon light like grooved steel, the space 
np in the lamina corresponding to the groove formed by the 
cutting diamond point in the metallic surface. 
