EVOLUTION BY EXPLOSION. 
283 
land than we observe a few taking to themselves 
wings; crude ones to be sure, but still a great advance 
upon the webbed foot. Then we find the primi¬ 
tive feather, wonderful in its adaptation to the air. 
The butterfly, gracefully floating upon the breeze, 
begins with the earliest flowers. Trees of exogenous 
growth suddenly spread over the land, and terrestrial 
animals in varied force follow each other upon the 
scene. Finally, man stands there in full stature. 
EVOLUTION BY EXPLOSION. 
As we have seen, life leaps into existence as it 
were with a bound. Many species and myriads of 
individuals seemed to originate in a comparatively 
short interval of time. Frequently thereafter, a new’ 
crop of species left forms in the preserving strata. 
Between these periods were long intervals of rest. 
These rest intervals have caused much trouble to 
theorists. Environment is ever present and ever ac¬ 
tive, and ought to have a constant influence upon the 
life forms. There should be a steady progression of 
life, a more or less regularity in the variations. How 
shall the rest periods and the quickening intervals be 
explained ? 
Dr. Stanfuss has long experimented with butter¬ 
flies, in order to discover the law of heredity. The 
results are considered important. He observed that 
sometimes an unusual richness in new varieties ap¬ 
peared, and has applied the expression ‘‘ Transforma¬ 
tion by Explosion ” to such an outburst. It was this, 
probably, that led M. de Vries to apply ^‘Evolution 
