The last contribution to the series of Catalogues was made in the room we have been examining. Its production was the constant labour of two years; and the volume contains exact particulars of many facts never before noticed. Amongst other things, for instance, made out with certainty in this place by Mr. Quekett, after months of patient investigation, was the elementary differences in the character of bone. To the common eye and common idea, all bone is simply bone; and for common purposes the word indicates closely enough what the speaker would describe. Not so to the naturalist and the physiologist; and so scalpel and microscope went to work: the sea, the land, and the air, lent each their creatures peculiar to itself, and the labour of the search was at length rewarded by a discovery that each great class of living things has an elementary difference in the bones upon which its structure is built up. Hence, when a particle of bony matter is now placed under the microscope, come whence it may—from a geological strata, or from the depths of the sea, or from within the cere-cloth of a mummy—the observer, guided by Mr. Quekett’s observations, knows whether it belonged in life to bird, beast, or fish. Glancing round this anatomical workshop, we find, amongst other things, some preparations showing the nature of pearls. Examine them, and we find that there are dark and dingy pearls, just as there are handsome and ugly men; the dark pearl being found on the dark shell of the fish, the white brilliant one upon the smooth inside shell. Going further in the search, we find that the smooth glittering lining upon which the fish moves, is known as the _nacre_, and that it is produced by a portion of the animal called _the mantle_: and for explanation sake we may add, that gourmands practically know the mantle as _the beard_ of the oyster. When living in its glossy house, should any foreign substance find its way through the shell to disturb the smoothness so essential to its ease, the fish coats the offending substance with nacre, and a pearl is thus formed. The pearl is, in fact, a little globe of the smooth glossy substance yielded by the oyster’s beard; yielded ordinarily to smooth the narrow home to which his nature binds him, but yielded in round drops—real pearly tears—if he is hurt. When a beauty glides proudly among a throng of admirers, her hair clustering with pearls, she little thinks that her ornaments are products of pain and diseased action, endured by the most unpoetical of shell-fish.