248 ANIMALS OF LAND AND SEA 



sides of the cones of the largest spouting geysers where they 

 were Hable to be washed away in a flood of boiling water. 



The maximum temperatures at which plants can exist have 

 been carefully determined, and it has been found that certain 

 of the so-called blue-green algae may occur in some abundance 

 in water with a temperature of over 154°, and they will even 

 live in springs with a temperature of from 167° to 170°, only 

 42° below the boiling point. Indeed they have been reported 

 from higher temperatures, up to 199°, though these records 

 need confirmation. Thread algae have been found in water 

 with a temperature of 176°. 



Animal life in such situations as these is, however, infrequent. 

 In fact most animals, even in the tropics, are rather sensitive 

 to excessive heat, especially dry heat. In a very hot and arid 

 part of Venezuela I noticed that certain beetles when disturbed 

 would drop at once to the ground, a common habit among 

 weevils and some other types, where, exposed to the terrific 

 heat of the sand, they soon died, victims of the only means of 

 escape from an enemy they knew. 



On the surface of the earth all living things exist under a 

 pressure of one atmosphere, becoming slowly less with increasing 

 altitude, which means that every square inch of our bodies is 

 continually under an air pressure of 14 3/4 pounds, and our 

 whole body under a pressure of about 14 tons. Water is about 

 814 times as heavy as air, so that in the sea the pressures under 

 which animals live are much greater than on land, and they in- 

 crease rapidly with depth — about one atmosphere for every 

 32.8 feet. What effect does this have upon the animal life in 

 the sea? Strange to say, practically none at all; at least the 

 effect is so much less than that of the changed conditions of 

 light and temperature and altered food conditions at great 

 depths that it is not evident. The bodies of sea animals 

 being composed mostly of water they may be said to be trans- 

 parent so far as that liquid is concerned. 



In the Pacific on the run between Yokohama and the Ha- 

 waiian Islands the "Challenger" made a successful dredge haul 



