12 REPORT—1858. 
The paraboloidal part of the lens, viz. ADBE, consists of paraboloidal lamine, the 
surfaces of which are perfectly smooth, and give no diffracted images by reflexion like 
the surfaces of the lamine of other lenses. The spherical portion, MNOP, consists 
of spherical laminz of the same character. The structure of both portions of the 
lens is fibrous, the fibres diverging from poles in the axis of the lenses, that is from 
one pole in each lamina of the two lenses. The fibres, however, must be perfectly 
flat in order to compose lamine perfectly smooth; and I have not been able to 
observe that they are united by teeth as they are in other animals. They must 
adhere, therefore, to each other by the contact of their surfaces merely, or by some 
structure not visible in the microscope, and not showing itself by its action upon light. 
The thin transparent membranes which cover the anterior convex surface of the 
paraboloid, and the concave surface of the spherical meniscus, have also a fibrous 
structure, the fibres diverging from a single pole in the axis of the lenses. The sur- 
faces which these membranes cover are the ends of all the fibres which constitute 
the leas; and each lamina terminates in a sort of ring or margin which is well 
defined. This ring is a little larger in diameter than the proper section of the para- 
boloid, and the consequence of this is that the fibres, or the termination of the lamine, 
are curved upwards, so that their surfaces are concave near the line DBE. 
The two lenses are curiously united. The concave surface MON is less than the 
convex one, DBE, and there is a notch between Dand M going round the lens. The 
meniscus is kept in its proper place, in contact with the paraboloid, by a ring abcd 
(fig. 3), in which ab=0'50 of an inch, and cd=0°31. 
In the Sepia Elcdona the whole lens is nearly spherical, as shown in fig. 4, the 
Fig 4.—Sepia Eledona. 
Fig 3.—Ring DE. 
a 
Fig. 5.—Figure by polarized light. 
axis or diameter AB being a little larger than mn, whereas in the Sepia Loligo it is 
smaller. The lens divides into two parts along maben, abc being a hemisphere about 
the ;/;th of an inch in diameter. The whole annular surface, from the circumference 
mn to a, C, is covered with two membranes, to which the ciliary processes are attached. 
In order to examine the polarizing structure of the lens, I made a section of it by 
two planes parallel to the axis, so that the plate was about the 15th part of an inch 
thick. When immersed in oil, it gave, in polarized light, the figure shown in fig. 5, 
when the axis of the lens po was parallel or perpendicular to the plane of polariza- 
tion. The tints to the left of v and w were the highest, namely the yellow of the 
first order. The sections 1, 2, 3, 4 are negative in reference to r, and 5, 6, 7, 8 are 
also negative in reference to the intersection between 6 and 7. When the polarized 
light is transmitted along the axis of the eye, a black cross is seen, as in uniaxal 
negative crystals ; but the cross opens upon turning round the section, indicating a 
defect of symmetry in the substance of the lens round the axis. The luminous por- 
tions at 5, 6 are very bright. 
When the lenses are quickly dried, the laminz separate from each other, and the 
lenses have the appearance of pearls; the resemblance is so great, that when the ex- 
periment is well made, it is difficult to distinguish them from real pearls, as will be 
seen in the accompanying specimens*. 
* These specimens were exhibited to the Section. 
