^^"^ ZOOGENESIS T^" 



So every living thing on land, whether plant or 

 animal, must have some provision to counteract the 

 variability in the available supply of water, and espe- 

 cially to guard against the loss of moisture. 



Thus all adult insects living in the open, like house- 

 flies, June-bugs, wasps, bees, moths and butterflies, 

 are protected by a tough impervious covering. 

 Among the backboned animals or vertebrates the rep- 

 tiles and the birds are best protected against the loss 

 of moisture. Consequently reptiles and birds with a 

 few insects having an insatiable thirst for nectar, sap 

 or blood are the characteristic creatures of hot and 

 extremely arid regions in the daytime. 



In the cool and relatively damp nights in the same 

 regions mammals take the place of reptiles, issuing 

 from their holes and other hiding places and ranging 

 widely everywhere, while many different kinds of 

 insects take the place of the very few that are abroad 

 by day. In less arid regions mammals become more 

 varied and abundant, and are seen by day as well as 

 after nightfall; birds and insects also become more 

 varied and abundant, and amphibians (toads) appear. 

 In still moister regions frogs are also found. 



The young of insects — maggots, grubs or caterpil- 

 lars, or, in the case of grasshoppers, bugs (fig. X3, 

 p. 33) and other types, small wingless replicas of the 

 fully grown — are always less well protected against a 

 loss of moisture than are the adults. The young of 

 house-flies, which live in moist decaying substances, 

 the young of June-bugs, which live in moist soil and 

 are commonly called "white-grubs," and the young 



[45] 



