170 Degeneratio7i in the Ostrich 



situated distally. Taken in conjunction with the other facts of degenera- 

 tion it is held that the rest of the scales on the fourth toe, which should 

 connect the remaining few with the tarsal system, have been lost to the 

 race, and are a phase of retrogression. It will be shown that the incep- 

 tion of a similar loss is taking place over the big middle toe, and may 

 be also taken to represent its first expression of degeneration. 



At the joint between the tarsus and big toe a definite break in the 

 scutellation sometimes occurs, and very rarely a second break over the 

 middle joint of the toe (PL VI, fig. 6). As in the fourth, the breaks 

 represent a distinct loss of scales. They are clearly new retrogressive 

 characters in course of introduction into the ostrich race. Out of 

 20 Cape birds of mixed breeding one only showed the discontinuity, 

 while in 20 mixed Nigerian birds a single break occurred in three cases 

 and a double break in two ; thus its introduction has proceeded some- 

 what further in the northern than in the southern bird. Where two 

 breaks occur only five or six scales remain between them, and should 

 these disappear the bi^ toe would have only a single distal series, about 

 seven to ten in number, and its scutellation would then be altogether 

 similar to that characteristic of the small one at the present time. 

 Therefore the stages represented by the big toe may in all likelihood be 

 taken to illustrate the manner in which the reduction in scales was 

 effected on a small toe, though the latter has retained no confirmatory 

 survivals. The losses have probably no adaptive significance whatever 

 and therefore no selection value. They are found on chicks on hatching 

 and while in the egg, and remain unchanged during the ontogeny of the 

 bird. 



Where numbers of ostriches are taken into account no sharp line of 

 demarcation is to be found between the continuous and the discontinuous 

 scutellation on the big toe. In some scarcely any narrowing of the 

 scales occurs at the first joint and none at the second, and from this all 

 stages in their reduction can be observed, first over one, and then over 

 both joints, their place being taken by the insignificant scales which 

 cover the lower part of the leg generally. As in former degenerative 

 series the many variations encountered are deemed to represent the 

 order according to which the retrogressive changes take place for the 

 race as a whole. An unexpected difference however obtains in the 

 manner of disappearance of the scales over the first joint as compared 

 with those over the second. In the former they simply become smaller 

 and smaller until they cease to be continuous, and then ultimately 

 disappear, the middle smallest going first, and the others in a regular 



