THE AMPHIBIA 305 



the loss or the mutilation of limb or tail, new parts rapidly grow 

 out, and they are not permanently inconvenienced by the loss. 



Hibernation. - - Many Amphibia bury themselves in the mud 

 at the bottom of ponds in the autumn, and remain there in a dor- 

 mant condition until the following spring. During this period 

 of hibernation the vital processes are reduced. No air is taken 

 into the lungs, since all necessary respiration occurs through 

 the skin ; and no food is eaten, but the physiological activities 

 are carried on by means of nutriment stored in the body. The 

 temperature of all cold-blooded vertebrates - - lampreys, sharks, 

 rays, fish, amphibians, and reptiles varies with the surrounding 

 medium. Frogs cannot, however, be entirely frozen, as is often 

 stated, since death ensues if the heart is frozen. In warm coun- 

 tries many Amphibia seek a moist place of concealment in which 

 to pass the hotter part of the year. They are said to sestivate. 



Poisonous Amphibia. - - The poison glands of the leopard 

 frog have already been mentioned (p. 253). The toads and 

 certain salamanders and newts are also provided with poison 

 glands. As a means of defense the poison is very effective, since 

 an animal that has once felt the effects of an encounter with a 

 poisonous amphibian will not soon repeat the experiment. No 

 amphibians, however, are harmful to man. 



The Common Toad. --One of the commonest and most 

 valuable of all amphibians is the toad (Fig. 186). This much- 

 detested animal is not responsible for all the evil things laid up 

 against it. It does not cause warts to appear on the hands that 

 touch it ; it is not poisonous ; and it will not, if killed, make the 

 cows give bloody milk, as is often believed in the country. On 

 the other hand, toads are not only perfectly harmless to man, but 

 are among the most beneficial of all animals because they de- 

 stroy harmful insects and slugs. They live in our gardens if 

 they can find a damp and hidden retreat, and they sally forth 

 toward evening in search of insects and other small animals, 

 most of which are injurious to vegetation. In twenty-four hours 

 the toad consumes " a quantity of insect food equal to about 

 x 



