but a key of the proper construction. It is a tumbler system because the impediments so placed upon the turning of the key are in fact tumblers packed round the cylinder of the key (retained by springs), and allowing the passage of the key-plate only when pressed down to the various depths to which each separate tumbler is adapted in order to provide an open passage for the key-plate all round. This union of ideas developed separately in different branches of the same trade, device or industry, corresponds to the crossing of individuals and breeds in nature, which is so necessary to reproduction. The analogy, as I have already intimated elsewhere, might be carried even further and closer if space permitted. It is a necessary condition of the absence of creative power in nature, and applies equally to all the processes of evolution whether of species or of ideas, but the subject requires broader treatment than can be given to it here. My object in writing this paper being to trace the development of particular forms rather than to generalise, I must leave the philosophy of the subject for separate treatment. From the foregoing description of the various kinds of primitive locks in use in different countries it will, I think, have been made evident that some of them most certainly have been derived from a common centre. The wooden key-drawn pin-locks have spread over the region extending from Egypt to Yarkand. The Scandinavian wooden locks of the same kind, though differing in the details of their construction, we have seen are common to Norway and Scotland, and by some means have been carried to the West Indies and British Guiana, whilst the tubular spring padlock of the Roman age in Europe is the same that is found throughout the whole region extending from Italy to China and Japan on the east, northward into England and Scandinavia, southward into Abyssinia, and westward into West Africa and Algeria, Spain, and on as far as the West Indies.