J. E. DUERDEN 151 



is hoped that it may be possible to attempt this, but with such a slow 

 breeding animal the number of years required is not an encouraging 

 contemplation. The building-up of a pure strain of the highest numbered 

 birds has a high industrial bearing, but the production of low-numbered 

 birds is a retrogressive step. 



With the remiges in their present degenerative phase, dropping out 

 in ordinal succession one after another from the elbow end of the row, 

 there should be no limit to which the losses may proceed, given the 

 required time ; they should continue until all the wing-quills have dis- 

 appeared, as is already the case with the second and higher rows of 

 under-coverts. It is otherwise however with any addition to the upper 

 limit. No degi'ee of selection can increase this if the factors were never 

 there ancestrally, or if they have been altogether lost to the race. As 

 43 plumes was the highest number previously encountered it was with 

 some surprise that chicks with 44 were found in the first series. A 

 margin of one or two is however to be expected in view of the considera- 

 tions already given as regards factorial variability and expression during 

 degeneration ; but it is highly questionable whether any further increase 

 will occur from the future mating of the highest numbered chicks. 



Leg Coverts. 



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

 provided with natal down feathers, similar to those over the wings and 

 body generally (PI. VI, fig. 3). They are merely tufts of barbs bearing 

 barbules, without any shaft, and in due course are pushed out by the 

 definitive feathers of the chick plumage. The pteryla usually persists 

 until the chick is about six months old, but from this time onwards 

 the feathers, complete in every way, gradually drop out without others 

 taking their place. The first to disappear are those over the outer 

 surface, followed by others along the sides, until when about a year 

 old the leg is entirely naked with the possible exception of a few odd 

 feathers along the posterior border, and rarely along the anterior border 

 (PI. VI, fig. 4). The rate of falling out and the number persisting vary 

 in different birds. The pits of the empty sockets are visible for many 

 years, gradually becoming less conspicuous^ 



1 It may be noted that after the adult plumage is attained in the ostrich at two or three 

 years, no external distinctions remain by which the age of a bird can be determined ; the 

 complete absence or otherwise of the contour feathers of the leg, as well as the freshness 

 of the pits of the empty sockets, are some approximate guide for the first few years. 

 Some farmers' birds are' known to be between forty and fifty years old. 



10—2 



