320 Proceedings of the Royal Physical Society. 



may be employed in its proper place amongst other data 

 used for classification. I take advantage of the present 

 opportunity also, to incorporate many new observations, as 

 well as to make some emendations to my former paper 

 suggested by a wider knowledge of the facts. 



The general conclusions may be conveniently stated at this 

 point. They are that a particular style of overlap or imbri- 

 cation of the several feathers in each row of the external 

 Cubital Coverts, and a particular number of feathers in each 

 row, are absolutely constant for all the individuals of the 

 same species, for all the species of the same genus, and even 

 for all the genera in the same family or even order as this 

 last is understood by ornithologists in general. For example, 

 over five thousand species of Passeres, embracing the whole 

 of the Acromyodi, and nearly all the Mesomyodi, exhibit 

 absolutely the same general style of wing coverts. This 

 style is not only uniform throughout the entire group, but is 

 absolutely characteristic of it, as it is not found in any group 

 of birds outside the commonly-accepted limits of the Passeres. 

 A glance at the wing of a bird will therefore enable one to 

 pronounce at once whether it belongs to a Passerine bird or 

 not. What is true of the Passeres applies also with more or 

 less truth to other groups of birds : each group being charac- 

 terised by its own special pattern. The exceptions, so far as 

 I have observed them, will be separately noticed ; and it will 

 be seen, in most cases, that it is more than likely that these 

 exceptions are more apparent than real, and that they are 

 more likely than not to be due to the birds in question 

 having been wrongly placed in the systems most in vogue. 



As a type Professor Flower has chosen the Wild Duck. 

 This is excellent of its kind ; but, having regard to all the 

 observed variations, the wing of the Golden Plover is by far 

 the better type (see Fig. 18). From this wing, by successive 

 slight modifications in different directions, every style of 

 wing coverts observed in the Euornithae may be reached by 

 easy gradations. But, as Mr Wray has taken as his type the 

 wing of the Wild Duck, I have added a drawing of it (Fig. 14), 

 which has been carefully drawn, and has been repeatedly 

 compared with other examj)les belonging to the same 



