258 RELICS OF PRIMEVAL LIFE 



it appear? Many of its higher forms, those which 

 depend upon animal food or on the more complex 

 plants for subsistence, would obviously be unsuit- 

 able. Further, the sea-water is still too much 

 saturated with saline matter to be fit for the higher 

 animals of the waters. Still further, there may be 

 a residue of internal heat forbidding coolness, and 

 that solution of free oxygen which is an essential 

 condition of existence to most of the modern 

 animals.' Something must be found suitable for 

 this saline, imperfectly oxygenated, tepid sea. Some- 

 thing too is wanted that can aid in introducing 

 conditions more favourable to higher life in the 

 future. Our experience of the modern world shows 

 us that all these conditions can be better fulfilled 

 by the Protozoa than by any other creatures. 

 They can live now equally in those great depths 

 of ocean where the conditions are most unfavour- 

 able to other forms of life, and in tepid unhealthy 

 pools overstocked with vegetable matter in a state 

 of putridity. They form a most suitable basis for 



* It has been assumed that any temperature over 120" 

 Fahrenheit would be incompatible with ordinary aquatic life. 

 bull such life is at least possible in some form up to 2oo^ 



