CHAPTER XXXVIII 



ANIMAL RESPIRATION— AMPHIBIOUS VERTEBRATES 



The term "amphibious" is often applied to creatures Hke 

 the Hippopotamus, which, though land-animals as regards struc- 

 ture, spend a large part of their time in the water. But, scien- 

 tifically speaking, this is on a par with the well-known definition 

 of an Amphibian as "an animal which cannot live on land and 

 dies in the water ", which utterance is supposed to have been 

 derived from a perennial source of oracular knowledge, i.e. the 

 answers to examination papers. Zoologists apply the term 

 amphibious to animals which throughout life are able to breathe 

 both air dissolved in water and ordinary air, or which carry on 

 the former mode of respiration during the earlier part of their 

 existence, becoming air-breathers in the limited sense when 

 adult. 



So far as backboned animals are concerned, it is convenient 

 to consider Amphibious Fishes in the first place, and then to 

 deal with Amphibians proper, such as newts, frogs, and their 

 kindred. 



AMPHIBIOUS FISHES (Pisces) 



There can be no doubt that land-vertebrates are descended 

 from aquatic ones, and since these last are typically represented 

 at the present day by fishes, it is among such animals that we 

 must look for transitional forms which help to bridge the gap 

 between the inhabitants of the water and the dwellers on land. 



Among Ordinary Bony Fishes (Teleostei) there are a number 

 of species which, though not properly speaking amphibious, are 

 very tenacious of life, and can exist for some time on land, if 

 surrounded by a damp atmosphere. It is among freshwater 

 fishes that this kind of peculiarity is best marked, and the Com- 

 mon Eel {Angui/la vulgaris) is the most familiar instance. This 



