REPTILES AND AMPHIBIANS II9 



element, which is due to the law of heredity, affects 

 animals far more profoundly than the common features 

 due to similar adaptations, which are generally external. 

 In our time it is sought to base classification 

 exclusively on the law of heredity, all animals being 

 regarded as a gigantic family and classified according to 

 their degree of kindred. Thus the classification of 

 animals has been intrinsically justified by Darwin. 

 The common element on which it is now built is 

 scientifically explained by the law of heredity. 



In the present chapter we have to deal with two 

 classes, the reptiles and the amphibians, and we can 

 do this the more easily as both classes have few 

 representatives in Europe. Reptiles and amphibians 

 require heat. The temperature of their blood rises 

 with a higher external temperature, and gives more 

 vigour to their vitality. Hence it is that we meet 

 more species of the two classes the further south we go, 

 and more highly coloured and powerful animals in 

 proportion to the length of summer in the district. The 

 giants of the reptile class and the largest amphibians 

 live in the moist tropical forests, where the rays of the 

 sun are almost unendurable to us. The serpents wind 

 through the bush like living branches of trees, the 

 crocodile lurks in the broad river for the animals that 

 come to drink, and the voices of the tropical frogs 

 resound at night like the roar of oxen. 



At one time it was different here. 



Many millions of years ago, in what are called the 

 Jurassic and Cretaceous periods, there were large 



