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 
" orthogeneti c saltation" (Fig. 395). 
451. Illustration of the Pendulum. The difference be- 
tween discontinuous and fluctuating variation may be 
Extreme 
Mean 
FIG. 396. Diagram to illustrate the difference between fluctuating 
variation and mutation; O, 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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