ECOLOGICAL FACTORS 383 



to the highest mountain peaks, such as the Kilimanjaro, Ruwenzori, 

 and Kamerun mountains. The buliminids, Cylindrus obtussus and 

 Mastus reversalis, which normally live in the Austrian and Transyl- 

 vanian Alps above the tree line, cannot be brought alive into the 

 lowlands by collectors. 



The number of eurythermal animals is much greater among the 

 land than among aquatic animals, as would be expected from the 

 greater temperature variations in the air. In this group belong many 

 insects, especially those with complete metamorphosis, for example 

 the Diptera with short antennae, many butterflies, as the white butter- 

 flies Pieris and the painted lady, Pyrameis cardui, whose world-wide 

 distribution shows their independence of temperature. Collembola, 

 e.g., the glacier flea, Isotoma saltans, are also eurythermal. Of the 

 Amphibia, the toad {Bufo bufo) is especially eurythermal; this species 

 is distributed from 65° N. latitude to north Africa, and ascends in the 

 Alps to an altitude of 2200 m. above sea level. In North America 

 Bufo fowleri ranges from Massachusetts to Georgia. 



Homoiothermy. — The homoiothermal or so-called warm-blooded 

 animals occupy a unique position. Physiologically they are plainly 

 stenothermal, because their vital parts are not exposed to air tempera- 

 tures, but to their own internal medium, in which an optimal tem- 

 perature of 37° to 44° (according to the species) is maintained with 

 but slight variations. With the exception of hibernating animals, the 

 body temperature variations are normally not more than about 4°C. 

 The pigeons (Columba) show a variation of 1.44°, the Adelie penguin 

 of Antarctica 2.8° (37.4°-40.2°), goats (Capra) 0.25°, rhesus monkeys 

 up to 3.8°; among the camels, temperature variations may attain a 

 maximum of 4.4°, which is very exceptional. 21 Only the most primitive 

 mammals, the monotremes, show greater body temperature variations ; 

 in Echidna it amounts to 7.5° (26.5°-34°) . Nervous regulation is neces- 

 sary to maintain a constant body temperature; cooling causes a reflex 

 increase of the oxidative processes in the body and consequently a 

 greater production of heat ; in rabbits the entire store of glycogen can 

 be caused to disappear by cooling. The body temperature of the arctic 

 ptarmigan, 43.3°, may be as much as 80° above that of its environ- 

 ment. The maintenance of a relatively high internal temperature frees 

 animals from the numbing influence of low temperatures. 1 The external 

 temperature becomes dangerous for a homoiothermal animal only when 

 it begins to affect the internal temperature permanently. 



The methods of internal temperature regulation depend upon 

 whether the external temperature is lower, approximately equal to, or 

 higher than the body temperature. In the first case we are concerned 



