Temperature 83 



higher temperatures (Hori, 1928). Shelf ord (1929) has suggested 

 that each type of animal requires a certain characteristic number of 

 thermal units to complete its life. 



The survival or the abundance of an animal in a particular 

 habitat may depend upon the extremes that temperatures reach. 

 Many animals can withstand temperatures below the freezing 

 point of water, but few live above about 40 °C. At Naples the 

 death of various marine animals was found to occur at temper- 

 atures ranging from 32.5 °C. to 43.5 °C.; variations probably be- 

 ing due to chemical and physical differences between species 

 (Vernon, 1899) . Most animals can change their upper limits 

 of temperature toleration somewhat by acclimatization (Hath- 

 away, 1927) . At Tortugas some marine and fresh-water animals 

 live in ponds where temperatures reach 42 C. or more (Pearse, 

 1932e) . On the New England coast high temperatures which 

 intertidal barnacles tolerate range from 23.4 to 27 °C. (Cole, 

 1929) . Tropical marine animals live near their maximum limits 

 of temperature toleration, and their activities are readily retarded 

 by cold (Mayer, 1914, 1918). When they die at high temperatures 

 it is apparently on account of acidosis and lack of oxygen to carry 

 on metabolic activities. 



The faunas of hot springs are derived from fresh water and 

 land. Typically marine animals are absent. "Furthermore the 

 preponderance of species related to ones that have migrated into 

 a marine or semi-marine (brackish) environment indicate that 

 thermal and saline situations have imposed similar obstacles to 

 the biota which has entered them from fresh water. These depend 

 undoubtedly upon the presence of salts in solution and the attend- 

 ant rise in osmotic pressure of the medium. High temperature is 

 a deterrent that has been overcome by acclimatization ordinarily, 

 however, within quite narrow limits, especially in case of animals, 

 which are able to endure much less heat than plants. An added 

 inconvenience is the rather consistent dearth of dissolved oxygen 



