532 Mr. Gr. L. Bates on the Reversed [Ibis, 



likewise agree very well, as to the facts, with the detailed 

 and extensive ones here to be recorded. He notes the vary- 

 ing tendency to be reduced in size, or to disappear, in 

 the different parts of these two series of feathers. The 

 different degrees of reduction or disappearance, together 

 with variations in the overlap, as observed in different birds 

 and groups of birds, with the manner of the derivation of 

 one condition from another, so far as that may be traced, 

 form the subject of the present paper. 



Before leaving the literature relating to the reversed 

 under coverts, it is proper to mention the important writings 

 of Goodchild (4, 5) on a similar subject, the cubital upper 

 coverts. In the different series of upper coverts ou the 

 cubitus he found variations characteristic of groups of birds, 

 particularly as regards their overlap. He introduced and 

 defined the terms "distal" and "proximal overlap," which 

 have been used also by other writers since. 



In the following pages another way of describing the 

 overlap is employed, and the terms "distal" and "proximal 

 overlap" are not used. I am aware that this terminology 

 should not have been discarded without ample reason. My 

 reason is that it is liable to ambiguity and confusion, in 

 more ways than one, and tiiat it not only may be, but 

 has been, used diflerently by different writers. The first 

 difficulty is that " distal overlap " does not tell us whether 

 the distal edge is the one that covers the edge of the other 

 feather, or the one that is covered by it. In the former 

 sense it is used by Goodchild ; but it is used in the latter 

 (and opposite) sense by Gadow both in Bronn^s ' Tierreich/ 

 chapter on Pterylography (p. 558), and in Newton's 

 ♦Dictionary of Birds,' article "Tectrices" (p. 951). But 

 still another chance for ambiguity arises, when the under 

 surface of the wing is considered as well as the upper one, 

 which alone was kept in view by Goodchild. Are we, tlien, 

 to view the underside of the wing as if held in the hand or 

 laid on a table, upside down, or in its natural position on 

 the bird ? The latter view can be taken only in imagination ; 

 but it is the consistent one if the whole of the feathering of 

 the wing is to be thought of at once, as should certainly be 



