112 WORLD-POWER AND EVOLUTION 



were liberating them the entire forest was covered with a greenish 

 jellow or brown dust. During the Permian Period the sharp 

 transitions from cold to warm, or from moist to dry caused these 

 ancient forests to die out. Conifers much like those of today 

 came into existence. Seeds largely took the place of spores. 

 These changes were accompanied by a general reduction in the 

 size and variety of the plants, and by a tendency for them to 

 become hardier and to have thicker and less ornate leaves. 



During the great climatic changes of the Permian, animal life 

 suffered an even greater transformation than plant life. For 

 example, previous to that time the insects had been of truly 

 astonishing size. Out of the 400 forms known in the early and 

 middle parts of the Pennsylvanian Period which preceded the 

 Permian, the smallest had wings over a third of an inch long. 

 The wings of more than twenty species were six inches long, six 

 attained to nearly eight inches, and three were giants of twelve 

 inches ! Imagine a spore-dusted forest full of insects as large as 

 crows! The cold and changeable climate of Permian times 

 apparently caused the extinction of all these forms. Their place 

 was taken by small species resembling those of today. Moreover, 

 the very nature of insects was profoundly modified by the intro- 

 duction of metamorphosis. That is, where there had formerly 

 been merely a gradual growth from the egg to the adult, there 

 was now a growth from egg to maggot or caterpillar, then a 

 resting period, and finally a transformation from maggot to fly 

 or from caterpillar to butterfly. At the same time the insects 

 acquired the power to become dormant and thus persist for months 

 at a time. All these changes apparently were due to the necessity 

 for adapting themselves to sudden periods of drought or cold 

 during the time of growth in summer, or to the necessity for 

 enduring long, severe winters. Thus the climatic variability of 

 the Permian Period not only caused a remodelling of the earth's 

 garment of vegetation, but introduced a unique stage into the life 

 history of insects. 



