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Show 230 DR. H. GADOW O N T H E [Mar. 15, degree of affinity between two or more species, genera, families, or larger groups of creatures. This I have tried to do in a manner hitherto not applied to birds ; it may have been done by others, but they have not published any account of this process. Certainly it has not been applied throughout the whole Class of Birds. I have selected about forty characters from various organic systems (see Appendix, p. 254), preferring such characters which either can be expressed by a formula or by some other short symbol, or which, during the working out of the anatomical portion of Bronn's ' Aves,' have revealed themselves as of taxonomic value, and of which I have learnt to understand the correlation, determining causes, and range of modification. Other characters, perhaps too complicated, too variable, or last, but not least, too imperfectly known in many birds, are left out or reserved for occasional employment. Of m y 40 characters about half occur also in Fuerbringer's table, which contains 51 characters. A number of skeletal characters I have adopted from Mr. Lydekker's ' Catalogue of Fossil Birds,' after having convinced myself, from a study of that excellent book, of their taxonomic value. Certain others referring to the formation of the rhamphotheca, the structure and distribution of the down in the young and in the adult, the syringeal muscles, the intestinal convolutions, and the nares, have not hitherto been employed in the Class of Birds. Groups of birds, arranged in bona fide families, sometimes only genera of doubtful affinity, were compared with each other- each family with every other family or group-and the number of characters in which they agree was noted down in a tabular form. Presumably families which agree in all the 40 characters would be identical, but this has never happened. There are none which differ in less than about 6, and none which agree in less than 10 points. The latter may be due to their all being birds. It is not easy to imagine two birds which would differ in all the 40 characters. In another table all the families were arranged in lines according to their numerical coincidences, and attempts were made to Arrange and to combine these lines of supposed affinities in tree-like branches l. These attempts are often successful2, often disappointing3. 1 Many calculations are obviously unnecessary: for instance, the comparison of Geese with Parrots or Passcres; Steganopodes with Swifts, Rollers, Trogons, &c. 2 For instance, Pteroclida? agree with Limicolse and with Columbae in about 29 points, with Alcce and with Gallidae in 24, with Ralli in 21, with Lari only in 18.-Again, Lari agree with Alcte and with Limicoke in 33 or 34; Limicoke agree with Alcas, Lari, and Ralli each in 33, with Pterocles and Columbaj in 30 or 31, with Gallida; in 2 & Combination of these lines shows that Lari and Pterocles are widely divergent from each other, while they each separately agree closely with the Limicolae; in other words, Lari and Pterocles are specialized in two different directions as terminal divergent branches of one common Limicoline stock. 3 The more generalized, or rather the less specialized, two given groups are, the more characters they will probably have in common, and similar false affinities will appear the more likely the greater the diversity of organic modifi- |
