J. E. DUERDEN 161 



entirety, nor have the various phalanges, but each has become slowly 

 reduced in size. On the face of it the conclusion seems irresistible in 

 favour of a gradual factorial weakening by changes of one kind or 

 another. The factorial degradation may be so great that it gains 

 somatic expression for only a brief period in the embryo and is not 

 continued even to the time of hatching. 



Plumes on Third Finger. The tip of the third digit, whether free 

 or hidden, extends nearly to the hind border of the wing, and at this 

 place one or two additional plumes sometimes occur, interfering with 

 the regularity of arrangement of the row of under-coverts and wing- 

 quills (PI. V, fig. 2). These irregular feathers are often a puzzle to ostrich 

 farmers, since from their size and position it is clear that they are 

 neither remiges nor coverts. Dissections show that they belong to a 

 distinct series, their internal quills crossing the phalanges of the third 

 digit in the same manner as the quills of the remiges cross those of 

 the second digit. Without doubt therefore they are to be regarded as 

 belonging to the former, though being situated near its tip they at first 

 give the impression of being under-coverts or wing-quills. 



In addition to the feathers at the tip, single plumes are on rare 

 occasions found set along the course of the buried digit. They may 

 appear at any part of its length, and are of .a distinct type from the 

 under-coverts. It is submitted that the one or two at the tip, along 

 with these single feathers, are survivals of a time when the ancestor 

 of the ostrich had its third finger fully provided with feathers, in the 

 same manner as the bastard wing. If this be the case, then the ostrich 

 is apparently the only living bird in Avhich the third digit still bears 

 feathers, though with the present facts before us there can be little 

 question that this was the condition in ancestral birds. 



The persistence of such a far remote ancestral condition in the 

 ostrich, altogether beyond what is found in other living birds, is some- 

 what remarkable considering the extent to which plumage degeneration 

 in general has already proceeded. It is probably to be associated with 

 the less degree of retrogression which the third finger has undergone. 

 Along with the discovery of an extra-cranial pineal vesicle at a certain 

 stage of development and a persistent pineal patch, it serves strongly 

 to emphasize the primitive nature of the ostrich in certain respects ; 

 also the slowness of the retrogressive changes going on in some directions 

 as compared with others, and their independence one of another. The 

 independence becomes all the more impressive when we consider the 

 degenerative stage reached by the digits of the wing compared with 



