234 ME. p. CHALMEES MITCHELL ON SO-CALLED 



in which one would not readily look for primitive features. 

 OpistJiocomus is an exceedingly peculiar and specialized form. 

 Among the Ealline birds generally, the three eutaxic forms 

 Fsophia, Dicholophus, and Mhinochetus present many striking 

 peculiarities which are not generally regarded as primitive, and 

 anatomists generally have regarded them as modified forms of the 

 diastataxic Gri'uidse. There remains the great group of Gallina- 

 ceous birds, which in many respects, such as the alimentary canal 

 and the completeness of the muscles, present primitive features 

 and are yet eutaxic. On the other hand, they are specialized in the 

 sternum and in the vertebral column. The Anseriformes, which 

 are diastataxic, are quite as primitive in their muscular structure 

 and less specialized in the sternum and vertebral column, while 

 among them are to be found the Palamedeidae, certainly archaic 

 forms, and sometimes regarded as forming a link between the 

 typical Anseriformes and the Gralli. These are diastataxic, as 

 primitive as the Gralli in muscular anatomy, more primitive 

 osteologically, and with alimentary canals displaying what 

 appears to be an exceedingly primitive disposition. So far as a 

 general survey goes, there is nothing against and a good deal 

 in favour of supposing that diastataxy is arch.itaxic in Aves 

 generally. 



The Alcedinidse and the Cypselidse are groups in which, as in the 

 Columbae, some members are eutaxic, while the others are diasta- 

 taxic. I have not had an opportunity of dissecting a suflficient 

 number of these forms to obtain an idea as to which condition 

 of the wing is associated with greater specialization. 



Summary. 

 The Columbae, which, have been regarded hitherto as a diastataxic 

 group, have several members with the eutaxic condition. Com- 

 parison of the feathering in these forms makes it probable, or at 

 least plausible, that the eutaxic condition has been attained by 

 closing up of the gap, with first crowding, and then disappear- 

 ance, of two of the three feathers occupying the primitive gap. 

 Intermediate stages between true wide-gapped diastataxic forms 

 and true eutaxic forms occur. Comparison of the anatomy of 

 the eutaxic forms with that of the diastataxic forms shows that 

 the former are on the whole more advanced in the general pro- 

 gressive modification of the whole group. It is easy to show 

 that in a hypothetical pentadactyle wing a gap in specialized rows 



