AMPHIBIANS. 205 



CHAPTER VII. 



AMPHIBIANS. 



THIS order of animals, while presenting certain features 

 such, for instance, as the cold blood, oval corpuscles, 

 and three-chambered heart, common to the Reptiles, has 

 several characteristics which are very distinctive. Leaving 

 out of consideration a few abnormal foreign species, it may 

 be well to sum up here those features which are found in all 

 British Amphibians, and to give under the heading of each 

 species only those peculiar to itself. The title "Amphibia" 

 is better than the obsolete " Batrachia," because it calls 

 attention to the fact that all the animals grouped under it are 

 amphibious in the sense that they spend part of their exis- 

 tence in the water, when they breathe by gills; and part 

 on land, when they breathe by lungs. They all undergo 

 metamorphosis: the young or larval forms are called tadpoles, 

 and in many respects present strong similarities to fishes, 

 breathing by gills which are at first external, afterwards 

 internal, and having a flattened fin-like tail which, however, 

 is not supported on bony rays. The tadpoles are in most 

 cases herbivorous, feeding chiefly on confervoid algae, but the 

 adults are always carnivorous. It is well-known that in all 

 animals that are herbivorous, the intestine is long, whilst in 

 those that are carnivorous it is short and simple. Strange 

 to say the Amphibia begin life with the intestine of the 

 herbivorous character, and as the metamorphosis progresses 

 this changes gradually to the shorter simpler form found in 



