EXPERIMENTAL EVOLUTION 



529 



When discontinuous variation proceeds along a definite 

 line through several successive generations, each step being 

 an intensification of the preceding one, it is designated 

 " orthogenetic saltation" (Fig. 395). 



451. Illustration of the Pendtilum. — The difference be- 

 tween discontinuous and fluctuating variation may be 



Mean 



Fig. 396.^ — Diagram to illustrate the difference between fluctuating 

 variation and mutation; 0, original point of suspension; M, new point of 

 *' suspension after the mutation has occurred. 



aptly illustrated by a swinging pendulum (Fig. 396). The 

 vertical position, assumed when at rest, is the mean of all 

 positions that may be assumed as the pendulum swings; 



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