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Mar., 1916 THE NEW MUSEUM O1? COMPARATIVE OOLOGY 69 anyone should ever have attempted to classify birds on the strength of variation in any single set of characters, whether of feather arrangement (pterylosis), feather structure, arrangement of muscles, or even of the bony structure itself. Position in any scheme of classification, that is, relationship and phylogenetic history, is determined by the sum of characters; and determination of the value of any one factor in development involves a knowledge of the rate of change. Certain strongly marked characters may have been so recently, that is, so rap- idly, acquired as to be almost valueless in determining the deeper, truer, his- torical relationship. Other characters, apparently no more distinctive, may yet really be so deep-seated, so little subject to change, as to yield conclusive testi- mony as to cousinships in the hoary eld. Now it appears that in the complex of evolved characters which go to make up a bird, although subject itself to a high variation, no single element is more stable, more conservative, more phylogenet- ically eloquent, than that 'of the egg. No single character of the egg, viewed externally, is negligible. Size, color, shape, texture, surface, number even,--all are eloquent of relationship and history. Save in the order Passeres, where the tendency to vary, long latent or suppressed in the egg, has burst into sudden and highly complicated efflorescence, a comparison of egg-shells is exceedingly instructive. This does not mean that comparative oSlogy is a substitute for com- parative myology, or comparative osteology, or even pterylosis; but it does mean that the egg has its ow? testimony to offer, and that it is able to throw a powerful side light upon history, and so upon the scheme of classification. So important is this claim that I pause to note a few instances. The class- ical example is that of the Laro-Limicolae. The older science, content with appearances, and deceived by homoplasy (that-is, the concurrence of forms superficially similar, issuing from diverse stocks, which have been acted upon by uniform conditions), had, in a sort of childish helplessness, ranged the Gulls and Terns alongside the Albatrosses and Petrels. Whereas a glance into any egg cabinet shows that the heavily-colored eggs of the Gulls and of the Shore-birds are so similar as, in so far forth, to proclaim unity of origin in the parents; while the single white egg of the Tube-nosed bird is at the farthest remove of an entirely different line of development. The oSlogist could have told (and did tell) at a glance what the older ornithology failed to discover. In like manner, the close relationship between the Herons and the Cormorants, testified now by the anatomist, but difficult of comprehension on the part of the casual observer because of the birds' very dissimilar appearance, finds instant confirmation in the drawer of the oSlogist. Eggs of the Black-crowned Night Heron could be palmed off for those of Baird's Cormorant, and vice versa. To take but a single insiance of a claim to which the anatomist has not yet consented: The oSlogist knows that the heavily-colored egg of a Loon represents age-long differentiation from the primitive uncolored type exhibited by a Grebe's egg. The separation between Loons and Grebes is a very ancient one; yet the anatomist, deceived again by homoplasy, and underestimating his own data of diverse osteological characters, allows the two groups, Gaviidae and Podicipedidae, to subsist in a single order, Pygopodes. That such facts are significant, there can be no question. They have by no means escaped notice; but they have not had a sufficient or an exhaustive con- sideration. The Museum of Comparative O51ogy proposes for its first task the assembling of such abundant and representative material as will enable Science to work out these problems with some degree of intelligence.