In the trifling paper I sent you respecting "Cats," which you deemed worthy of insertion in No. 398, you have it "by some merchants from the Island of Cyprus, who came hither for _fur_," it should be _tin_--Fur being an article of importation. * * * * * BOOKSELLERS' MARKS OR SIGNS. (_For the Mirror_.) Many books, especially those printed in the 17th century, have no other designation either of printer, bookseller, or even city, but merely marks or signs. The _anchor_ is the mark of Raphelengius, at Leyden; and the same with a _dolphin_ twisted round it, of the Mantuii, at Venice and Rome; the _Arion_ denotes a book printed by Oporrinus, at Basil; the _caduceus_, or _pegasus_, by the Wechelliuses, at Paris and Frankfort; the _cranes_, by Cramoisy; the _compass_, by Plantin, at Antwerp; the _fountain_, by Vascosan, at Paris; the _sphere_ in a balance, by Janson, or Blaew, at Amsterdam; the _lily_, by the Juntas, at Venice, Florence, Lyons, and Rome; the _mulberry-tree_, by Morel, at Paris; the _olive-tree_, by the Stephenses, at Paris and Geneva, and the Elzevirs, at Amsterdam and Leyden; the _bird between two serpents_, by the Frobeniuses, at Basil; the _truth_, by the Commelins, at Heidelberg and Paris; the _Saturn_, by Collinaeus; the _printing press_, by Badius Ascensius, &c. P.T.W. * * * * * THE NATURALIST. * * * * * DIFFERENT COLOURS OF THE EGGS OF BIRDS. It is a remarkable fact in the economy of nature, that of those birds whose nests are the most liable to discovery, and whose eggs are most exposed to observation from the form of the nests, the eggs are of that colour which is the least different from the surrounding objects; whilst those birds whose eggs are of a bright and positive colour, hide their nests in the hollows of trees, or never quit them, excepting in the night, or sit immediately that they have laid one or two eggs. It is also to be observed that of those species which build an exposed nest, and the females of which alone perform the duty of incubation, the colour of the female is much less bright than that of the male, and more in harmony with the objects by which she is surrounded during the period in which she sits upon her eggs. It would seem, therefore, that those birds which lay a brightly-coloured egg have the instinct to make a close nest, or to place it in the least exposed situations; while those which lay a sober-coloured egg are less solicitous to conceal it from the notice of their enemies. M. Gloger, a German naturalist, has paid great attention to this curious circumstance, and has very recently published an elaborate memoir, in a work printed at Berlin, in which he notices the habits of all the species of birds indigenous to Germany, in confirmation of the theory. Our limits will not allow us to notice the particular species which he enumerates; but it may be sufficient to