86 WHAT EVOLUTION IS 



was this that led Weismann and 

 others to experiment in this direction. 

 Colonies of mice and of rats were 

 subjected to mutilation and were 

 then used for breeding with the view 

 of ascertaining whether such mu- 

 tilations were heritable. Thus the 

 lengths of the tails of a number of 

 adult white mice were measured, their 

 tails were then cut off, and they were 

 used as breeding individuals for a 

 new generation. When the second 

 generation had matured, their tails 

 were in turn measured and cut off 

 and a third generation was produced 

 from them. After the breeding of 

 approximately twenty such genera- 

 tions, all of which had been subjected 

 to the amputation of the tails at an 

 appropriate stage, the tails in the final 

 generation were found to be as long 

 as those in the first generation. Such 

 mutilations, then, gave no evidence 



