234 



MARINE ANIMALS 





temperature, less markedly on the salinity of the water. Other condi- 

 tions being equal, it is only half at 25° what it is at 0°. The conditions 

 for suspension of organisms are consequently more favorable in the 



Fig. 58. — Various sizes of Challengeria species according to the depths at 

 which they occur: A, Challengeria xiphodo7i; B, Ch.slogetti;C,Ch.naresi. X 140. 

 After Haecker. 



cold waters of the polar regions and of the oceanic depths than in the 

 warm tropical waters. It is possible, and even probable, that the great 

 pressures which prevail in the depths (almost 500 atmospheres at 

 5000 m.) affect the viscosity of water by causing association of the 



