J. K. DrKRDKN 171> 



havi' als<i Ihh'Ii (Muisidonsi in tin* li^ht t»f n'ViTHioiis to an jurlicr jinc<«Htrv, 

 but fulliT con»i»li'niti»»n Kwl.s uh to arcount. r>r thrm otlHTwJHr. l{<'tM'nt 

 «>hm;rvation8. to Ix* fully <l«'»tTil>e<i in a later j)a|Mr, hav«' shown that th«* 

 •xttrirh pn^s«'ntss us with nunurouH stji^os iinlicatin^ thr roui-sv of llw 

 dojjoiuTation which the win^ and Io^h have undcr^on*' up to thr jurm-nt. 

 118 well as tho course likely to hr followed in thr futun'. Survivals of 

 many antH»stnd chanictcristics an* to In- found ainon^^ th«* plmtifid 

 nmt<Tial now availahh* for study. Thus, while ordinarily only on<' in- 

 complete^ row of undcr-coverts is present, a fanner's strain exists in which 

 a second row of under-covertHS is almost complete, ami several memlx-rs 

 of a thin! row also <x*cur. and single m<'mhers of both rows are (K-c;ision- 

 ally met with on other birds. All slaves are t<» Ix* found from a complete- 

 niw of under-coverts to the usual (»ne where H to 10 are wanting at one 

 endof therow(Pl. Vll.fig. 2); and conditions of a like nature are to be met 

 with in the second row of upper-coverts. Vestigial down is to l>e found 

 on most ostriches over the wings and tail, though it is usually stated to 

 be absent. Further, while usually burie<l in the Hesh of the wing, the 

 thin! digit sometimes beai-s a second phalanx and projects freely from 

 the surface, and even bears its own plumes, a primitive conditi<^n sug- 

 gestive of the fossil bird Archneupteryx. The claw is usually absent 

 from the small, fourth toe of the foot but still survives in a few ; while 

 the sciiles on the middle toe show the beginnings of loss by one or two 

 breaks in their continuity (Text-fig. 2, p. 182). Experiments hitherto 

 carried out all indicate that the individual losses have proceeded as 

 retrogressive mutations, (»n definite factorial lines and in well-defined, 

 determinate directions. 



In view of all these survivals of many of the earlier characteristics 

 of the ostrich the 42-plumed bird may with good reason be regarded as 

 a survival of a stage when the average number of plumes to the wing 

 was larger than at present. On this interpretati<m the 36-plumed birds 

 of to-day are to be considered as degenerate in the number of wing quills, 

 as they are in many other respects. The practical endeavour is now- 

 being made to build up a pure strain of ostriches bearing 42 plumes, for 

 with the increase of the other njws of plumes in correlation with the 

 wing (juills it bec«jmes possible to provide the farmer with an ostrich 

 giving about 25 more plumes than he receives from his birds at 

 present, the "quality j)oints " being also of the highest. The demon- 

 strati«>n below that the high number is not merely the extreme of a 

 fluctuating series, but is factorial in its nature, renders this possible. 

 Whether bv continued s«'lecti(»n thi' number 42 will ever be exceeded 



