The crystalline lens of the eye, which is soft in quadrupeds, and cartilaginous in fishes, is very solid in the cephalopoda. It is almost calcareous, and very peculiar in its form. It consists of two double concave portions, divided by a deep groove, in which are inserted the ciliary processes. The two halves, which are almost globose at their outer surfaces, separate easily, and exhibit internally a series of concentric coats, which reflect light with a beautiful nacreous opalescence and play of colours. In some parts of Italy the women use these lenses as beads for necklaces. I have seen them thus worn at Genoa on festival days. They appear also to have been used as ornaments by the ancient Peruvians. Dr. J. E. Gray, in his “_Spicilegia Zoologica_,” published in 1828, says that the Rev. Mr. Hennah brought to this country several of a large size which he found in the tombs and old habitations of the natives; and that Mr. Stutchbury had informed him that the Sandwich Islanders sold these lustrous eyes to the Russians as pearls. The “cuttle-bone” or dorsal plate of _Sepia_, sometimes called “sea-biscuit,” from its shape and its being frequently found floating on the surface of the water, is used, when pounded, as polishing powder, by jewellers, and, under the name of “pounce,” to smooth writing-paper where an erasure has been made with a penknife. Known as “white coral powder,” it used to be regarded as the very best dentifrice,[29] and was formerly prescribed in medicine as an antacid and absorbent. The Roman ladies employed it, burned and pulverised, as a cosmetic for the face; and it was, no doubt, a good substitute for the “pearl powder” now in fashion. Broken pieces of it are also occasionally placed between the wires of the cages of song-birds, for them to peck at, instead of chalk or other calcareous substances.