J. E. DUKRDKN 1H<» 



As alretuly pn»vwi both tlu* iiorthtTii and th«* nouthorn hinln showing 

 the mutation Iwhuve i\» heti^rozygoU's in crosses. 



Like the loss of the scales from the middle toe the loss of the claw 

 on the fourth Uh» is a degenerative change in pr^gn'ss within th«* ostrich 

 race as a whole; likewise it is germinal in its nature, and in crossi's 

 follows Mendelian lines. Also it can readily Ix; mlmitted iis jwirt of an 

 establishfHl degenerative scheme which has Ix'cn going on in the fiH)! 

 for a viu<t jK»riod si^eing that the first, second and fifth toes have already 

 di8apjK»are<l. The loss is however an individual une, not oim* affecting 

 the race as a whole simultaneously ; but compariMl with that ot the sailes 

 the absence of the claw has reached a stage where by far the majority 

 of the race an^ aftected. The loss <»f the claw factor may be deemed to 

 take place de notv> in individual biixls, and in course of time has affectiMl 

 largiT and larger numbei*s. In crosses the presence of the claw is 

 dominant over it« absence, but, from the small pro|)<>rtion of individuals 

 now possi^ssing one, the chances of a clawed bin! mating with another 

 • clawed bird must be very remoU* ; hence, as the investigations prove, 

 the few showing the claw are heterozygotes. 



The fact that a germinal change, such as is involved in the loss oi 

 the claw or the scales on the toe, occui-s in individual birds anywhere 

 throughout the continent, strongly suggests that, whatevt'r the degeneni- 

 tive influence may be, it acts on the germ phism of the ostrich as a whole, 

 wholly irrespective of environmental conditions. It gains expression de 

 novo at different times in different individuals, but in the end affects all 

 the members of the genus, as had happened in the case of the losses 

 already sustained. The gradual loss of the scales, as well as that of the 

 claws and feathers, indicate that retrogressive evolution is taking place 

 piecemeal on strictly factorial lines, but in a continuous determinate 

 manner as regards the race. If, as seems likely, we are to regard the 

 baldness of the northern bird as the first step in the loss of the head 

 plumage then we have an instance of the retrogressive changes affecting 

 only one of the species (divergent mutations), while the loss of the scales 

 and claw is in progress for the entire race (parallel mutations). 



The parallelism of the changes going on in both species of ostrich is 

 readily understood if we regard the two as having a common origin from 

 the same germ plasm, with all its inherent tendencies. Many <>f the 

 parallelisms of evolutionary changes found in other forms of life may 

 also be deemed to be indications of a distant common origin for part at 

 least of their germ plasm. Darwin in his ()ri(/in, \). ITH, remarks: "As 

 all the species of the same genus are supposed, on my theory, t«» have 



18—2 



