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Show 360 MR. H. C. SORBY ON THE [May 4, A few eggs are of a brick-red colour. Those of Cetti's are as good an example as any I have seen; and on carefully comparing them with the browner red eggs of the common Grouse, I found that both contained a large amount of oorhodeine, but that the tint was made more dull in the case of the Grouse by the presence of a small quantity of the colouring-matter which gives the narrow bands in the red ; whereas in the case of Cetti's Warbler this was almost or quite absent, and there was present a relatively very unusually large amount of the orange-coloured substance, which I have not been able to distinguish from lichnoxanthine. To the presence of this substance we may thus attribute the brick-red tints seen in a few eggs. CONNEXION BETWEEN THE COLOURING-MATTERS OF THE EGGS AND THE STRUCTURE OF THE BIRDS. M y studies of colouring-matters by the spectrum method soon led me to perceive that the individual species of certain groups of coloured substances are so intimately connected with their life that plants may be arranged in a kind of natural order according to the presence, absence, or relative proportion of the various coloured constituents, which order on the whole agrees remarkably with that founded on structural characters, as shown in m y paper on comparative vegetal chromatology.* This naturally led me to consider whether any such connexion could be recognized in the case of birds' eggs. Much remains to be learned before any positive opinion can be expressed ; but what is already known appears to be sufficient to prove that, if there be any definite connexion between the general organization of birds and the coloured substances found in their eggs, it is not of such a kind as is at all obvious to any one who, like myself, is not thoroughly acquainted with anatomical details. Six out of the seven different colouring-matters occur in variable amount in a very great variety of eggs, but there is no greater variation than is met with in the different individual eggs of the common Guillemot; so that the study of the colouring-matters cannot be looked upon as of any value in distinguishing species, or even much wider groups, except, perhaps, in one particular instance. Hitherto I have met with rufous ooxanthine only in the eggs of the Tinamous, and perhaps in those of some species of Cassowary ; and though the question needs further examination, it is perhaps desirable to give a short account of what is already known. The eggs of the black variety of the common Duck are coloured with a nearly black substance, which I have not yet obtained in a state of solution, and which may correspond to the so-called pigmentum nigrum ; but whether it is a simple substance or a mixture remains to be determined, and therefore it would be premature to class it with the other more typical colouring-matters. EGGS OF THE TINAMOUS. As previously described, rufous ooxanthine when in solid form in * Proceedings of the Royal Society, xxi. p. 442. |