1886.] 



CUBITAL COVERTS OF BIRDS. 



201 



Gypagiis, I have been so much impressed with the uniform style 

 of wing-coverts prevailing amongst this group, that it seems to me 

 difficult to believe that their genetic relationship amongst them- 

 selves is more remote than Forbes regarded it. I cannot, after many 

 years' observation of the facts referred to in this paper, help re- 

 garding this similarity of style of wing-coverts in birds so different, 

 both in outward form and in their mode of life, as presenting us 



Fig. 34. 



Sarcorhavi])hus. 



with a certain amount of evidence of the transmitted survival, in an 

 unmodified form, of a mode of imbrication of epidermic structures 

 that at some remote period in the genetic history of the common 

 Sauropsidan ancestors of these birds played some really important 

 part in the economy of the wearer. During the differentiation of 

 such parts of the creature's organization as were directly affected by 

 the struggle for existence, other parts, not so affected, either 

 changed at a slower rate, or else were transmitted from generation to 

 generation hardly modified at all. Habit, or mode of life, as birds 

 now live, can at the most have played but a minor part in bringing 

 about these diversities of style. We have but to compare the 

 Swallows with the Swifts, the Sun-birds with the Humming-birds, 

 and many other parallel cases, and we at once perceive that mode 

 of life has had little or nothing to do with the origin of the features 

 in question. The real cause lies deeper than that, and dates back 

 far into the remote history of the Sauropsida. 



Reverting to the normal Ciconiine style of coverts, we find PlataJea, 

 with Ibis and its allied genera, differing but little from each other 

 and from Ciconia. 



Tantalus, in this respect, stands nearer to the Limicolae. 



The Cranes, again (fig. 35, p. 202), present another variation little 

 removed from the central Pluvialine type. 



Somewhere near to the Cranes and the Storks, but connected in 

 some way with the Gallinaceous style of coverts, stands the wing of 

 the Secretary Bird (fig. 36, p. 202); it is quite unlike (he true 

 Accipitrine type. 



Proc. Zool. Soc— 1886, No. XIV. 14 



