230 DR. H. GADOW ON THE [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 my 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 accord- 

 ing to their numerical coincidences, and attempts were made to 

 arrange and to combine these lines of supposed affinities in tree-like 

 branches ^ These attempts are often successful^ often disappointing ^. 



^ Many calculations are obviously unnecessary : for instance, the comparison 

 of Geese with Parrots or Passeres ; iSteganopodes with Swifts, Rollers, Trogons, 

 &c. 



^ For instance, Pteroclidse agree with Limicol^ and with ColurabEe in about 

 29 points, with Alcai and with Gallidse in 24, with Ealli in 21, with Lari only 

 in 18. — Again, Lari agree with Alcaj and with Limicolte in 33 or 34 ; Limicolse 

 agree with Alcai, Lari, and Ealli each in 33, with Pterocles and Columbas in 30 

 or 31, with Gallidas in 26. Combination of these lines shows that Lari and 

 Pterocles are widely divergent from each other, while they each separately agree 

 closely with the Limicolis; in other words, Lari and Pterocles are specialized in 

 two different directions as terminal divergent branches of one common 

 Limicoline stock. 



^ 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- 



