CONDITIONS OF LIFE 241 



on end and thawing out again as the spring approaches in 

 an active condition. It is recorded that one of these fishes was 

 swallowed frozen by a dog, thawed out in the stomach, and 

 vomited up alive. Dr. Gill describes how he kept some little 

 Mud Minnows {Umbra) in a large glass jar of water, which froze 

 solid during an exceptionally severe spell of weather, the jar 

 being broken. The lump of ice was allowed to melt gradually, 

 and every one of the fishes revived and swam about in a new 

 receptacle in a perfectly normal manner. Marine fishes have 

 also succeeded in adapting themselves to low temperatures, 

 and quite a fair number of species are found in Arctic seas, 

 although a mere handful as compared with the number found 

 in tropical and temperate regions. In the Antarctic there is a 

 fairly rich fish fauna, even within the limits of the pack-ice. 

 At certain seasons of the year some of these circumpolar fishes 

 live in water that is at or very near to freezing-point. Many 

 oceanic fishes must also endure very low temperatures, the 

 deeper layers of the oceans being at the most three or four 

 degrees Fahrenheit above freezing. 



Few, if any, marine fishes are able to endure water of any 

 great heat, but some fresh-water forms, and particularly the 

 inhabitants of tropical swamps, are able to live in water which, 

 during certain seasons, becomes considerably heated. The 

 hot-springs of Arabia, many of them containing water which 

 feels hot to the hand, all serve as dwelling-places for swarms of 

 tiny Cyprinodont fishes (Cyprinodon) , apparently unharmed by 

 the high temperature. A small Cichlid ( Tilapid) found in large 

 numbers in Lake Magadi, in the bottom of the Rift Valley, 

 Kenya Colony, is especially interesting. This lake is com- 

 pletely isolated, and the fishes occur in the thermal springs of 

 soda liquor on its eastern shore. The temperature varies in the 

 dififerent springs, but the fish seem to thrive equally well in 

 water, or rather soda, ranging from 80° F. to 120° F. 



Although certain kinds of fishes are able to survive in waters 

 of extreme temperature without apparent hurt, it must not be 

 supposed that this is always the case, and actually the range 

 of temperature in which the average fish can live in comfort 

 is comparatively limited, about 12° to 15° for most species. 

 Some experiments conducted by two French scientists on such 

 well-known forms as the Roach (Rutilus), Tench {Tinea), 

 Gudgeon {Gobio), Bleak {Alburnus), and Eel {Anguilla) are of 

 interest. They subjected individuals kept in aquaria to varying 

 temperatures, carefully noting their behaviour in every case, 



