SOME RESULTS OF OSTRICH INVESTIGATIONS. 2"] }^ 



the ostrich is the only living bird in which the third finger bears 

 feathers, though there is little question that this was the condition 

 in ancestral birds. 



Upper-Coverts. 



The upper-coverts are black in the cock and grey in ihe hen, 

 and alternate with the wing-quills. (PI. 4B.) The number of 

 rows varies somewhat ; in some birds only two or three are well 

 defined, but five or six in others. As regards the number of 

 plumes to the row, the first one varies in direct correlation with 

 the wing-quills, and shows no independent reduction ; the second, 

 on the other hand, is in a degenerative phase at its distal end, in 

 contrast to the proximal end of the first row of under-coverts. 

 Very rarely the second row bears the full number necessary for 

 complete alternation with the first, or has only one or two less; 

 often six or seven, or even as many as ten are missing, but all 

 intermediate stages are to be met with. Occasionally some of 

 the terminal feathers are vestigial, as if undergoing piecemeal 

 degeneration. The rows of upper-coverts are usualh/ more 

 reduced in northern than in southern birds, the wing as a whole 

 being then appreciably narrower. It is evident, therefore, that 

 the actual number of rows of coverts is undergoing reduction, as 

 well as the number of plumes in each as far as the second. The 

 degenerative influence has not yet reached the first row of 

 coverts, except in so far as it varies with the wing-quills. 



Lcg-C overt s. 



In the newly-hatched chick the outer surface of the fore-leg is 

 provided with natal feathers similar to those over the wings and 

 l3ody generally, and in due course these are pushed out by the 

 feathers of the chick plumage. The full covering persists until 

 the chicks are about six months old, and from this time onwards 

 the feathers gradually drop out without others taking their place, 

 until when about a year old the leg is entirely naked, witli the 

 possible exception of a few feathers along the posterior border, 

 and rarely along the anterior border. The rate of falling out 

 and the number remaining vary in difl:'erent chicks. The pits of 

 the empty sockets persist for years, gradually becoming less 

 conspicuous. 



In this case we may hold that the germinal factors concerned 

 with the production of the leg-coverts retain their normal activity 

 until the chicks are about six months old, and then by far the 

 greater number lose their effectiveness, and the feathers fall out. 

 Were we to seek an adaptive explanation, the loss might be 

 associated with the increased size of the wing plumes. While the 

 latter are small, the outer surface of the leg would be 

 uncovered were it not for its own coverts. As the chicks become 

 older the wing quills grow longer, and, in extending downwards 

 and backwards, serve to cover the fore-leg; hence it may be held 

 there is no further need for their presence. There may be .some 

 adaptive need for them in the young chicks, but not in the older 



