AMPHIBIA 253 



trial habits are assumed (Fig. 105, B). Most salientians 

 breathe as much through their soft moist skins as 'through 

 the lungs. On this account they are able to endure pro- 

 longed submergence; the blood being aerated through the 

 skin from the surrounding water. 



Self-protection. Though toads have bitter, poisonous 

 secretions in the skin, they are eagerly eaten by snakes, 

 owls, and other animals. They escape from many enemies, 

 however, by doing most of their hunting in the early morn- 

 ing or at twilight, and hiding in their holes during the day. 

 Hopping is a somewhat erratic method of locomotion and 

 toads are hence often able to elude a pursuer. Their colors 

 also render them relatively inconspicuous, and may change 

 somewhat to match different backgrounds. 



Salientians have less power of regeneration when adult 

 than salamanders. If a foot is lost, it does not grow again, 

 but the leg remains a deformed stump. The tadpoles of 

 frogs and toads are rather remarkable for their ability to 

 replace lost parts, and continue to grow after serious in- 

 juries. Eight- and ten-legged frogs, two-tailed tadpoles, 

 and other monstrosities have been produced by splitting 

 embryonic structures. It is also possible to form composite 

 tadpoles by grafting parts of different individuals together. 



On account of their terrestrial life toads cannot remain 

 active during the winter like the strictly aquatic am- 

 phibians. At the approach of cold weather, they burrow 

 into the ground below frost and remain in a torpid condi- 

 tion. During hibernation metabolism is very slow and 

 many activities are dormant; a toad may be cut in pieces 

 without giving any sign of life. 



Race Preservation. Toads show one great advance in 

 complexity of mating instincts when compared with a 

 salamander they make use of sounds. In order to insure 

 the continued existence of any race of animals, the eggs 

 must be fertilized and any adaptation which tends to make 

 this more certain is therefore desirable. In spring when 

 the male toads enter the ponds and utter their shrill notes 



