CHAPTER II 



LARV^ AND METAMORPHOSES 



The easiest way to begin to get a picture of the group of young 

 animals which are very unhke their parents is to remember that 

 many animals now live in surroundings quite different from those 

 of their remote ancestors. Although frogs are able to swim well 

 and often are found in water, they are really land animals. They 

 have lungs and breathe air, they hop about on land in search of the 

 beetles and other insects on which they feed, and many of them, 

 especially the green tree-frogs, never readily take to water except 

 at the breeding season, and others even lay their eggs on land. 

 The ancestors of frogs were fish-like animals, living entirely in the 

 water, with gills, not lungs, with a swimming tail and without hands 

 and feet. Probably in the course of a long period of time, and while 

 they were stiU aquatic animals, some of them began to swallow air 

 in the way that a number of fishes still get an additional supply of 

 oxygen, and probably also some of them had pouches on the gullet 

 into which the air was taken, as in the lung-fishes which still live 

 in the waters of Africa, Australia and South America. Many 

 different kinds of fish crawl on their fins over the mud at the bottom 

 of the water in which they live, whilst others creep out on the 

 edge of the shore and hop along in the surf. It is not at aU difficult 

 to follow in imagination the slow changes by which such creatures, 

 living in shallow marshes, became more and more apt for terrestrial 

 life and thus truly amphibious, capable of living in water or out 

 of it. A long swimming tail is an inconvenient possession on land. 

 Newts and salamanders retain it, but are seldom able to move 

 quickly, and the fortunate ancestors of the frogs probably lost it. 

 The modern frog, however, instead of remaining amphibious, makes 

 the change from aquatic life to terrestrial life quickly, in a few days. 

 It hatches out as a tadpole, a fish -like creature with the head and 

 body in a single mass, continued behind into a long tail which is 

 adapted for swimming by the presence of a thin web above and 

 below. It has no limbs, and little tufts of gills protrude through 



C.A. 17 B 



