" QUINTOCUBITALISM " IN THE WIJTQ OF BIRDS. 233 



liave put larger dots to represent the actual quill-series of modem 

 birds. The primaries are the enlarged series of the index digit ; 

 the carpal remex belongs to the pollex series ; the next four 

 secondaries belong to the digital series of the four digits ; then 

 comes a diastataxic gap due to the alteration of curvature (as in 

 the transition from the neck to the body series in a Barcheli's 

 zebra) being bridged over by a wedge ; then follow the other 

 secondaries, whicb. are members at different levels of the suc- 

 ceeding diagonal rows. Natui-ally this supposition is entirely 

 theoretical, but it is enough to show that the occurrence of a 

 gap after five quills is a phenomenon which might have arisen in 

 a very simple fashion. 



So far as the underlying bones are concerned, the gap in my 

 diagram occurs much more distally than in the adult ordinary 

 bird. I do not think, however, that this presents the slightest 

 difficulty. We know that ontogenetically and phylogenetically 

 the wing of birds elongates. Actually in development the feather- 

 papillae shift along the wing. Superficial skiu-areas generally are 

 exceedingly primitive in their character, but may shift almost in- 

 definitely in their topographical relation to underlying structures. 

 In the human body, these changes of skin-area in topographical 

 position have been worked out in relation to the phenomena of 

 referred pain. 



Eutaxy and Diastataxy in Aves generally. 

 I am not at present prepared to extend the argument from the 

 Columbse to birds in general at length. But I may point out 

 that there is a general parallel to be found between the relations of 

 eutaxy among Columbine forms and the relations of eutaxy 

 among birds generally. In Columbine forms the majority are 

 diastataxic, and the few eutaxic forms are isolated among their 

 diastataxic congeners. Among the great groups of birds most 

 are diastataxic. We may leave out of consideration the Struthious 

 birds and the SpheniscidcB, as in these the wing is so greatly 

 modified as to make any comparisons misleading, especially as we 

 cannot be certain whether the modifications are from a high, or 

 from a very low type of wing. As for the other eutaxic forms, 

 the great majority of anatomists would agree that the Passeres 

 were extremely specialized birds, and therefore forms in which, 

 if diastataxy be primitive, one would not expect to find it. 

 Similarly the Pici, the Cuculidae, and Opistliocomus are birds 



