We find insects which may be considered altogether as concentrated colouring matter; among these, the cochineals especially are celebrated; with regard to these we observe that their mode of settling on vegetables, and even nestling in them, at the same time produces those excrescences which are so useful as mordants in fixing colours. 649. But the power of colour, accompanied by regular organisation, exhibits itself in the most striking manner in those insects which require a perfect metamorphosis for their development--in scarabæ, and especially in butterflies. 650. These last, which might be called true productions of light and air, often exhibit the most beautiful colours, even in their chrysalis state, indicating the future colours of the butterfly; a consideration which, if pursued further hereafter, must undoubtedly afford a satisfactory insight into many a secret of organised being. 651. If, again, we examine the wings of the butterfly more accurately, and in its net-like web discover the rudiments of an arm, and observe further the mode in which this, as it were, flattened arm is covered with tender plumage and constituted an organ of flying; we believe we recognise a law according to which the great variety of tints is regulated. This will be a subject for further investigation hereafter. 652. That, again, heat generally has an influence on the size of the creature, on the accomplishment of the form, and on the greater beauty of the colours, hardly needs to be remarked. LIII. BIRDS. 653. The more we approach the higher organisations, the more it becomes necessary to limit ourselves to a few passing observations; for all the natural conditions of such organised beings are the result of so many premises, that, without having at least hinted at these, our remarks would only appear daring, and at the same time insufficient. 654. We find in plants, that the consummate flower and fruit are, as it were, rooted in the stem, and that they are nourished by more perfect juices than the original roots first afforded; we remark, too, that parasitical plants which derive their support from organised structures, exhibit themselves especially endowed as to their energies and qualities. We might in some sense compare the feathers of birds with plants of this description; the feathers spring up as a last structural result from the surface of a body which has yet much in reserve for the completion of the external economy, and thus are very richly endowed organs. 655. The quills not only grow proportionally to a considerable size, but are throughout branched, by which means they properly become feathers, and many of these feathered branches are again subdivided; thus, again, recalling the structure of plants. 656. The feathers are very different in shape and size, but each still remains the same organ, forming and transforming itself according to the constitution of the part of the body from which it springs. 657.