ME. E. DEGEN ON EODTSIS. 393 



him on p. 290, I.e., thus: — ". . . leurs grandes couvertures qui sont pour le yoI un 

 element important les accom])agnent tOKJours dans leur chute" ^ These researches led 

 him also to the statement, recorded for the first time, of the two opposing directions 

 which these coverts on the cubitus pursue for their renewal, as the flight-feathers ; 

 and further that here (on the cubital part) they are developed in advance of their 

 respective remiges (see p. 290, I. c). 



To what extent this latter and more general statement is correct may be verified 

 from the facts as they appeared in connection with the part dealing with these feathers. 

 The degree of advance, as could be seen, depends upon the age of the individual. 

 The moult of the coverts also follows the direction of the flight-feathers. This direction 

 is not one of opposition from the extreme points of the forearm, but one which 

 converges for the distad and the medial groups, and one which diverges for the latter 

 and the innermost group. Gerbe did not investigate the appearance of the minor 

 series of coverts. 



Chalmers Mitchell's (12) interpretation of the longitudinal appearance of the flight- 

 feathers and their principal coverts is that they are the co-serial members of a 

 diagonally transverse arrangement with the other coverts, like that existing for the 

 scaling in Eeptiles, and as further diagrammatized by him in his text-figure on p. 232, 

 I. c. This on p. 230 he explains thus : — 



" . . . . the quills and major coverts appear first as horizontal rows. It is only when 

 these become obvious, and when one or two other longitudinal rows appear from 

 before backwards, that the diagonal rows begin to be marked, 6cc." 



And continuing further: — ■ 



" .... I am not, however, prepared to attach great importance to this early onto- 

 genetic appearance of the longitudinal rows as such." 



As the result of this investigation also shows, there is in reality a marked transverse 

 or vertical element entering into the composition. Though but faintly indicated in 

 the chick's first perennial wing-feathering, it gradually increases with every subsequent 

 moult by which the bird attains to perfect conditions of maturity and age. This 

 transverse arrangement is a survival, therefore, of the phylogenetic affinities which link 

 the present Class Aves to their Saurian ancestry. 



The horizontal or longitudinal sequence of growth of the rows, applied to every 

 series of the coverts (as well as the main quills) in their entirety, is the result of a 

 secondary provision, and of a purely ontogenetic origin, which is assumed by the 

 embryo and the young bird for its first set of wing-feathers. 



Afterwards this same sequence of renewal becomes restricted to those sections of the' 

 rows which form part of the several groups on the forearm. Within these groups- 

 the horizontal renewal is retained throughout every moult. Each of these three 

 sections performs this longitudinal process independently of the other two. 



' The italics are mine. 



