."^lO MUTATIONS AND EVOLUTION. 



regards any one of the retrogressve stages, but the results hitherto 

 warrant the expectation that pure lines can be extracted, except 

 in so far as degradation happens to be in progress. As regards 

 most of the losses, it is extremely doubtful if adaptation or the 

 welfare of the bird is in any way involved, and therefore natural 

 selection can in no measure be held to be directing their course. 

 It is inconceivable, for example, that the gradual loss of single 

 plumes in an ordinal sequence from the row of under-coverts 

 or elsewhere can have any discriminative bearing on the welfare 

 of the bird. Moreover, the losses have proceeded, and are 

 proceeding, on similar lines throughout the continent, showing 

 an independence of environmental conditions, and impelling one 

 to regard them as wholly intrinsic, presumably the result of some 

 inherent condition of the common germ plasm of the race, or 

 some consistent influence acting upon it. 



A completed retrogression, for instance, the loss of the 

 first and second toes, may be conceived as being of advantage to 

 the bird in the matter of rapid locomotion ; but no such considera- 

 tion can be ascribed to the many intermediate stages by which the 

 process has been effected ; and yet it is by the summation of small 

 successive changes that all the losses have been made. For 

 example, the claw on the small fourth toe is so reduced that 

 it never reaches the ground, and, as it is entirely functionless, 

 its presence or absence can have no selection value. It has 

 already disappeared from about 75 per cent, of the birds, and 

 the various intermediate stages still remaining: reveal that its 

 loss is in progress in the comparatively few individuals in which 

 it yet survives. On mechanical grounds an adaptive value may be 

 accorded the retention of only the middle toe when the small 

 fourth disappears, as in the case of the horse ; but, as unquestion- 

 able evidence is forthcoming that degeneration has already begun 

 on the third, its continuance would certainly dispel any idea that 

 the welfare of the bird is involved. A progressive or retro- 

 gressive change may incidentally be beneficial to a certain stage, 

 but harmful when continued further. 



It has often been pointed out that for a mutative series, 

 whether progressive or retrogressive, to be directed by natural 

 selection step by step, it must have a welfare value from the 

 beginning, and also at each succeeding stage ; but this is altogether 

 improbable as regards the degenerative series in the ostrich. 

 Unless selection can be invoked we must contemplate succes- 

 sional internal changes, say, of the nature of a regular methodical 

 degradation of some highly complex chemical combination, such 

 as the factors are deemed to be, changes uninfluenced by external 

 circumstances and without any concern for the welfare of the 

 individual. It is suggested that the degradation may be of the 

 nature of a slow senescence of the constituents of the germ 

 plasm, perhaps involving the Ratitae as an entire sub-class, for 



