578 Mr. G. L. Bates on the Reversed [Ibis, 



Rudimentary major under coverts usually absent on the 

 cubitus, and when present, only a few were found, and those 

 always at the proximal end next the elbow-joint. 



Conclusions. 



The account of the detailed examination of reversed under 

 wing-coverts having now been finished, it remains to con- 

 sider how far the several modifications discovered can be 

 seen to be derived from each other and from a primitive 

 type — in other words, to consider their bearing on a phylo- 

 genetic classification of birds. This is too difiicult a matter 

 to be gone into very extensively here ; but enough may be 

 said to show its importance and induce future study. 



The most primitive type of reversed under coverts found 

 in the birds examined is undoubtedly the one described 

 first, as the normal type found in some birds that cannot 

 all be considered as closely related to each other — the Ducks, 

 Scissor-bills, Plovers, and Sandpipers, — in which there is 

 a complete series of major, and a long series of median 

 coverts, the former all with conforming, the latter all with 

 contrary overlap. This most primitive type found, however, 

 may fairly be supposed to be derived from one still more 

 primitive, existing in the remote ancestry of birds, before 

 the large flight-feathers became much ditferentiated from 

 the ordinary covering feathers, in which both the series that 

 have now become the reversed under coverts had the same 

 uniform (conforming) overlap as the other rows that became 

 the remiges and the large upper coverts, and both extended 

 completely to the tip of the wing. The great development 

 of the large flight-feathers would cause a reduction and 

 partial disappearance of the less important of the two rows 

 in question, the median under coverts, at the narrowest part 

 of the wing, the tip. In no bird examined were the median 

 under coverts found to extend much beyond half-way on 

 the manus. 



The assumption of the contrary overlap by the median 

 coverts was the next step, and may be accounted for by a 

 consideration of the way in which they best fulfil their office 



