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



manual major under coverts is controlled by two opposite 

 tendencies, that towards efficiency, and that towards con- 

 formity with the remiges resulting from crowding, the latter 

 tendency acting most strongly near the tip of the wing. 

 Hence the place of the change of overlap on the manus is 

 indefinite, and great variation appears even among indi- 

 viduals of the same species, and sometimes between the two 

 wings of one bird. 



Conformity with the remiges as the result of crowded 

 situation is evidently the explanation of the universally con- 

 forming overlap in the manual major under coverts of 

 Passeriform birds ; for here the crowding is carried to the 

 greatest extreme, the major under coverts being set close 

 against the quills of the remiges, and no room is left for 

 them to take the contrary overlap. In regard to the less 

 degree of efficiency of these under coverts in Passeriform 

 biids, wliich we should hardly expect to find in view of the 

 high power of flight among them, it may be noted that in 

 this order of birds the coverts in general are of less size 

 and importance as compared with the remiges than in other 

 orders, and efficiency has been secured through the broad 

 and well-knit vanes of the remiges, the covex'ts being, as it 

 were, neglected. 



As intimated above, it seems sij^nificant that the major 

 under coverts so often begin to assume the contrary overlap 

 near the place where the median coverts cease — about the 

 carpal joint, — as if it were essential that there should be 

 everywhere one row overlapped in the way contiary to the 

 remiges. According to this, we should expect that in birds 

 having only the major series, the overlap would tend to 

 become contrary. The Plantain-eaters have only the major 

 under coverts, and they are always conforming ; but 

 Plantain-eaters are not birds that make great and con- 

 stant use of their wings in flight. Cuckoos, that fly more, 

 have likewise only the major under coverts, and these have 

 the contrary overlap, in many cases, not only on the manus 

 but on the cubitus also. It is significant that among 

 Accipitrine birds, all the numerous specimens examined of 



