194 Sir David Brewster on the Anatomical and Optical 
Dr. Young supposed, by any nerves or filaments whatever : 
on the contrary, it floats as it were within the capsule; and in 
holding the lens in my hand, I observed its axis of revolution 
take a horizontal position whenever it was placed in an in- 
clined direction. This observation I repeated many times with 
the same lens, though I have not been able to do it with others. 
When the lens is taken out of its capsule, and the softer 
parts removed by rubbing it between the finger and the thumb, 
we obtain a hard nucleus, the structure of which we shall now 
proceed to examine. In order to get rid of Soemmerring’s 
objections, I have often removed the recent lens from a newly 
caught fish, and taken out the nucleus without exposing it to 
any process of maceration or induration. I then detach a film 
or two from the nucleus, and find it to consist of regular trans- 
parent laminz of uniform thickness, and capable of being se- 
parated like those of sulphate of lime or mica. The surface 
of these laminz is perfectly smooth, and reflects light as co- 
piously as any other polished substance of the same refractive 
power*. 
When we look with a microscope at the surface of any la- 
mina, before it has been detached, it has the appearance of a 
grooved surface, like mother-of-pearl, or one of Mr. Barton’s 
iris surfaces; and in large lenses it is often easy to trace these 
apparent grooves or lines to the two poles of the axis of revo- 
lution, the lines being widest at the equator, and growing nar- 
rower and narrower as they approach the poles. In small 
lenses, however, it is extremely difficult, and often impossible, 
to follow these lines to their points of convergency by the use 
. . to} . 
of the microscope ; and hence both Leeuwenhoek and Sattig 
maintained, that in fishes the points of convergency formed: 
a line at each pole, the line at the one pole being perpendi- 
cular to the line at the other. These lines are bisected by 
the polar point, and the parts of the line on each side of the 
pole are called septa. Hence the lines or fibres which com- 
pose the laminz are related to two septa in fishes, according 
to Leeuwenhoek and Sattig. 
In examining these phenomena, I observed the surface of 
the lamine sparkling with the colours of mother-of-pearl +, 
and upon applying a microscope, adjusted to such a focus as 
to show distinctly the reflected image of the candle, I observed 
* The objections urged by Soemmerring may be still more completely 
removed by examining the lenses when newly taken out of the eye and im- 
mersed in a glass trough of distilled water. In many cases the septa and 
the fibres will be distinctly seen before it is possible that the lens could 
have undergone any change whatever. 
+ ites colours may be transferred to wax, &c., like those of mother-of- 
pearl, 
