J. E. DUERDEN 137 



missing, or are represented by small, degenerate feathers on the way to 

 disappearance. Hence while in most ostriches the under-coverts show 

 retrogression only at the proximal or elbow end of the row, in some few 

 a loss is beginning at the distal or free end also. 



From the details submitted it is apparent that the single row of 

 under-coverts in the ostrich is in process of gradual reduction, mostly at 

 the elbow end of the row, but to a less degree at the distal end also. 

 The alternative would be to regard the conditions encountered as repre- 

 senting the fixed normal fluctuations for the row ; but the occun-ence of 

 vestigial feathers, and other facts to be presented, show that losses are 

 actually taking place, and leave no doubt that retrogression is in progress 

 in many directions. Even if the losses are not actually taking place at 

 the present time they must have occurred at some period during the past 

 history of the ostrich, and in the ordinal manner which they now dis- 

 play. The number of birds available renders it possible to trace all the 

 stages from the rare complete row to one where as many as ten have 

 disappeared, indicating that the process has not proceeded uniformly in 

 all the representatives of the race. In most cases the absences involve 

 complete feathers, but the occasional presence of the diminutive and ves- 

 tigial members serves to prove that each loss has been brought about in 

 a slow continuous fashion, according to a definite sequence. 



Second and Third Rows. While- by far the majority of ostriches have 

 only the single, incomplete row of under-coverts, birds are occasionally 

 found which bear feathers belonging to a second, and even to a third 

 row. These additional feathers are more likely to be found on southern 

 than on northern birds. In one Cape cock as many as thirteen alter- 

 nating smaller plumes constitute a second row, and in front of these are 

 four other plumes alternating with them, and manifestly members of a 

 third row. They tend to give to the wing an appearance of a completely 

 covered under-surface, altogether different from the usually naked effect. 

 In other ostriches detached feathers of the second and third rows may be 

 present at any part of the row, or several may appear in regular suc- 

 cession, the middle members of the row being more likely to occur than 

 those towards the end. Only on one farmer's strain however have the 

 nearly complete second and third rows been found, and they re-appear 

 in the progeny, in more or less the same numbers. The feathers are 

 nearly always fully formed and, like the first three rows of upper-coverts, 

 are successively smaller from the first to the third row ; occasionally, 

 however, vestigial examples occur, representing degenerative stages of 

 individual plumes. 



