^^ THE NEW EVOLUTION f^'^ 



counterbalanced by uncanny ingenuity. On a calm 

 warm day in the late summer you will often see a little 

 spider standing on a stone or post with the abdomen 

 elevated and spinning out a thread or group of threads 

 of silk which by the warm air rising up the sides of 

 the stone or post is carried upward. When the spider 

 feels a strong enough upward pull from the rising 

 threads of silk it lets go its hold and is drawn up into 

 the air often to a great height where it is wafted about 

 for a greater or lesser distance before it comes to 

 earth again. 



It should perhaps be mentioned that there are many 

 caterpillars which in their youngest stage are provided 

 with numerous long hairs. Such, for example, are 

 the caterpillars of many of the moths in which the 

 females are incapable of flight. These caterpillars 

 are wind distributed after the same fashion as the 

 seeds of the milkweed and the dandelion, and the 

 young of spiders. 



Flight in one form or another is common to about 

 two-thirds of all known kinds of animals, and to 

 about three-fourths of all the kinds of animals in- 

 habiting the land. Most creatures fly simply in order 

 to get rapidly from place to place, but some, like 

 dragon-flies, most bats, and many of the birds, are 

 especially adapted to feed on other flying things. 



Being much heavier than air, a greater or lesser 

 part of the food of plants and all of the food of animals 

 lies on the ground or buried in the ground or sup- 

 ported by it. It is therefore fixed in its position. To 

 utilize this food land animals and plants must be 



