AMPHIBIANS. 211 



gills being no longer required now shrink up and disappear, 

 Simultaneously with the development of the lungs and 

 atrophy of the gills, a remarkable change takes place in the 

 circulatory system ; as long as the animal was a gill-breather, 

 it had a heart consisting of two chambers only one auricle 

 and one ventricle as in Fishes ; as soon as it becomes a 

 lung-breather the heart develops a second auricle, and then 

 consists of three chambers, as in most reptiles. Truly we 

 here see a wonderful transformation or rather series of 

 transformations quite as marvellous as the change from 

 the caterpillar to the butterfly. It has often been stated 

 that the tail and gills of the tadpole drop off when it passes 

 into the adult form: this is incorrect they are gradually 

 absorbed. The length of time taken for the whole pro- 

 cess of development varies according to circumstances. 

 Temperature is the most important factor ; in warm weather 

 it may be completed in eight or nine weeks ; in cold seasons, 

 possibly twice as long. Newts, however, are very much 

 longer than Frogs or Toads in reaching the adult stage 

 frequently retaining the larval form till the following year. 

 The differences between the spawn and tadpoles in Frogs, 

 Toads, and Newts may be tabulated as follows : 



FROGS. TOADS. NEWTS. 



Spawn deposited.. 



Tadpoles 

 Develop first .. 



In shapeless 



Hind Limbs 



In long strings . . 



Hind Limbs 



Singly in leaves, 

 or a few only to- 

 gether in a string. 



Fore Limbs. 



It is stated that the tadpoles of the Great Warty Newt 

 are not strictly vegetarians, but will devour insects and the 

 tadpoles of their smaller cousins. Comparatively few tadpoles 

 ever reach maturity for they are eaten greedily by the adult 

 newts, as well as by many water-insects, birds, and fishes, 



