ALPINE ANIMALS 501 



in increased metabolism, and may tend to save it from fatal freezing, 

 since frogs recover from freezing if the heart itself is not frozen. The 

 newt Triturus alpestris ranges to 2500 m., and the viviparous Sala- 

 mandra atra ranges up to 3000 m., and does not occur below 850 m. 

 The duration of development in S. atra is two years at lower levels 

 and probably three in the alpine zone. 50 In the Himalayas and western 

 Szechwan, the curious pelobatid frog, Aelurophnjne mammata, ranges 

 to an altitude of 4500 m. 



Reptiles are so characteristically stenothermal warmth-positive 

 animals that the low temperatures of the alpine zone exclude most of 

 them. In the Alps only three species reach the alpine zone: the vivip- 

 arous lizard to 3000 m., the common viper to 2750 m., and the blind- 

 worm to only 2000 m. The grass snake, Natrix natrix, ranges up to 

 1650 m., but this is below timber line. The three alpine species, be- 

 longing to very diverse groups, are all viviparous, and this is the 

 characteristic that makes possible their entry into the cold alpine zone. 

 There would not be enough heat to bring reptilian eggs to complete 

 development, while the viviparous female lizard or snake is able to 

 follow and keep the sun. The same three viviparous species are the only 

 reptiles found in Scotland, though there are egg-laying forms in Eng- 

 land. The highland chameleons of Central Africa, ranging up to 3200 

 m., 51 are viviparous. The common African skink, Mabuya varia, also 

 viviparous, ranges up to 4000 m. on Kilimanjaro. The lizards of the 

 genus Phrynocephalus in central Asia are oviparous at low altitudes* 

 and viviparous at higher levels.f 52 On Mount Orizaba in southern 

 Mexico, the iguanid lizard, Sceloporus microlepidotas is oviparous 

 at the base and viviparous at high levels, the eggs at intermediate 

 levels doubtless undergoing part of their development in the mother's 

 body. In Chile certain iguanids,$ ranging to 3000 m., are also vivip- 

 arous. 53 More lizards than snakes range into the alpine zone. 



Shortening of the limbs appears to characterize some of the skinks 

 (Leiolopisma) in the mountains of western China, and great reduction 

 or disappearance of the auditory apparatus is frequent in both frogs 

 and lizards of the same region. 



Homoiothermal animals are much more independent of the tem- 

 perature limitations of high mountains than are the cold-bloods, but 

 are still limited by oxygen and food requirements. It is astonishing 

 with what scant food the alpine mammals are able to live — the power- 



* P. jorsythi and P. axillaris. 



f P. erythrurus and P. theobaldi. 



t Liolaemus biirgeri and Phymaturus palluma. 



