DISTRIBUTION AND HABITS 1S1 



seizing or masticating the food but serve to hold it firmly and 

 prevent its escape from the jaws. The tongue is a great de- 

 velopment of muscle in the floor of the mouth attached to the 

 modified branchial skeleton ; it makes its first appearance in 

 Amphibia in the vertebrate series and is thus evidently called 

 forth by the requirements of terrestrial existence, that is to say, 

 fishes seizing their food under water, although they can move the 

 ventral parts of the gill-arches in taking food, do not require a 

 specialised muscular tongue and in the most aquatic Amphibia 

 the tongue is rudimentary or wanting. This organ is present 

 in all Amphibia except the Aglossa among the Anura, but is 

 least developed in the aquatic Urodela. It is most developed 

 in the Anura except the Aglossa, which are entirely aquatic, 

 and in which the tongue has been secondarily lost; in the 

 Discoglossidae it shows its most primitive condition adherent 

 by the whole of its base and incapable of protrusion ; in the 

 remaining forms it is developed into a long posterior process 

 which is turned forwards and rapidly withdrawn in the 

 capture of prey. It is a common characteristic of Anura that 

 they will not take any food unless they see it move; any one 

 who has reared tadpoles knows that they live and feed well 

 enough until the metamorphosis is completed, but that it is usu- 

 ally impossible to feed and rear the young frogs after they have 

 left the water. The only way to do this successfully is to put 

 small pieces of meat on the end of a wire and make them 

 vibrate in front of the little frogs which will then lick off the 

 morsel with their tongue. 



Salt is fatal to Amphibia, the eggs and larvae are killed by 

 a solution of even i per cent. They are therefore unable to live 

 in or to cross seas, salt lakes, or saline plains, although they may 

 occasionally be carried across seas in floating vegetation. Many 

 species are unable to live in waters containing much lime in solu- 

 tion, but others flourish in such waters ; the water in which Pro- 

 teus lives, for instance, flowing through limestone caverns, is 

 necessarily saturated with lime salts. Terrestrial Amphibia can 

 tolerate high temperatures with moisture but not cold and 

 drought. As we have seen, Anura abound in the moist forests of 

 the tropics ; in the water they are quickly killed by a temperature 

 above 40 C. or 104 F. but in the air a tree-frog can sit exposed 

 to the sun at a temperature of nearly 50 C. or 122 F. In this 



