218 EXPERIMENTAL EVOLUTION LECT. 



may be transformed into each other, or that the 

 characters upon which they are based are worthless 

 and require a severe revision. 



To end with external characters, I shall merely 

 remind you of the facts which illustrate the influence 

 of environment on integuments ; merino sheep lose 

 their wool in warm climates and recover it under cold 

 skies ; Iceland cattle have short and small horns which 

 develop well under mild temperature ; the silky cover- 

 ing of the common hen, in Guinea, becomes trans- 

 formed in Europe into the feathers we are accustomed 

 to see on our domestic fowl, etc. Such instances are 

 very numerous, and since the anatomical change 

 follows immediately upon the change of conditions, 

 we are at liberty to ascribe the former to the latter. 



But we must now turn to more important changes 

 in internal structure or functions, which may be 

 experimentally produced at will through environ- 

 mental changes. 



Schiibeler has shown that seeds may, through a 

 change in climate and environment, be made to 

 become larger than usual, and also to exhibit 

 greater rapidity in the germinating process. At the 

 same time the plants grown from the seeds are 

 more coloured than in their accustomed climate. This 

 fact may be ascribed to the influence of the greater 

 light in northern regions, and light, it is known, is apt 



