332 



THE AMERICAN NATURALIST 



[Vol. LIII 



them is inconceivable, and we are justified in concluding 

 that in the past the germ plasm has changed frequently 

 and presumably over a long period. Moreover, we can 

 hardly admit that the various degenerative phases will 

 remain as they are at present, but that further losses in 

 the same direction will follow, that is, the germ plasm will 

 continue to undergo retrogressive changes of a like 

 character to those already initiated. We may have an 

 appearance of continuous change, but when analyzed it 

 will be found to proceed by means of separate factorial 

 steps. It is conceivable that a continuance of the kind of 

 factorial losses now in progress will result ultimately in 

 the complete disappearance of the wings and legs of the 

 ostrich, allowing that the bird could survive the inter- 

 mediate stages, a postulate which it must be conceded is 

 of no mean order. May we not suppose that the limbless 

 condition of snakes and some lizards, amphibians and 

 fishes has come about by the successive losses of germinal 

 factors in a similar manner to that whicli is lioro shown to 

 be taking place in the ostrich? 



The bearing of the germinal changes involved in the 

 degenerative processes upon the thesis of Section \ V. rwny 

 be noted. It is in the highest degree improhnhlc ilint 

 determinate losses of such a widely emltraclN i- nnlnif are 

 taking place in response to any environmental stress 

 acting upon the germ cells; rather they may be regarded 

 as the result of some wholly internal physiological cause. 

 If due to environmental stress one could reasonably ex- 

 pect that in any individual the losses would be taking 

 place in all directions simultaneously, and would have 

 reached about the same degree in all. But among the 

 various rows of feathers, as well as in other parts, the 

 greatest independence in reduction is met with, as if the 

 factors for each were subject to a separate rather than a 

 common influence. 



VT 



''Mixing of germ p!ns„i.^ m (> i tiliintioii nJtns hrrrr]- 

 itary determiners mutiaiUii <iiid In'iio: is, in (ntd of itself, 



