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In describing the various structures which exist in the crystalline lenses of animals, I shall proceed from the most simple to the most complex combination of fibres. In the paper which I have already submitted to the Society, I took the lens of the cod as the type of thefirst or simplest structure, in which the fibres, like the meridians of a globe, converge to two opposite points of a spheroidal or lenticular solid; and I shall now proceed to describe thesecond or next simplest structure, as exemplified in the lenses of the salmon and the hare. This structure is shown in Plate IV. fig. 1, where A A is the anterior and B B the posterior hemisphere of the spheroidal lens of the salmon. A lens thus constituted is said to havetwo septa at each pole, A and B (fig. 2.), namely, the septa Ab , Ac , and Bd , Be , in different points of which all the fibres have their origin and termination. One of the fibres, for example, which has its origin in A, passes over N, and terminates ind ; while the other passes from A to O, and terminates ine . In like manner, the fibre which begins atb passes over P, and ends in B; while the fibre which begins atc passes over M, and terminates in B. The different parts of these four fibres lie in one plane, like the meridians of a globe. All the other fibres, which have their origin between A and B, have their termination betweend and B; and all those which have their origin between A andc have their termination betweene and B. All these fibres, or every fibre in each lamina exceptfour , have their different parts lying in different planes, or form curves of contrary flexure. In order to understand this structure, and appreciate its beauty, it is necessary to draw the fibres upon a globular surface. A perspective view of such a globe is given in fig. 3, where Ab is one of the anterior septa, and Bc one of the posterior ones. The two curves which go from the poles A and B to the ends of the septac, b, are ellipses, while all the rest are curves of contrary flexure.

VI. On the anatomical and optical structure of the crystalline lenses of animals. Continued from a former paper (Phil. Trans. 1833, p. 332.)