EXPERIMENTAL EVOLUTION T/F.CT. 



hardly estimate the number of the forms of life, it is 

 impossible to obtain any idea of the enormous 

 although finite number of the individuals. How 

 many plants were required to form a square foot 

 of coal ; and of how many Protozoa and sponges 

 is a cubic inch of chalk the only vestige ? Who 

 could dare to form an estimate of the number 

 of organisms which have disappeared and died with- 

 out leaving a single vestige, whose bodies, through 

 the slowly disintegrating processes of decomposition, 

 aerial or submarine, have abandoned their elements 

 to the atmosphere, the water, and the soil, the 

 materials of life whence they have unceasingly re- 

 turned to new organisms in the course of that circulus 

 which, like life itself, knows neither rest nor immo- 

 bility ? The very elements which at the present 

 moment are parts of ourselves, of our bones, of our 

 flesh, of our blood, brain, or nerve, were part, not 

 very long ago, of our ancestors further back still, 

 of prehistoric man ; and in a remote past, of that 

 inconceivable number of organisms of part of which 

 the sedimentary strata are the enormous burial-ground. 

 And when we come to consider that the circulation 

 of matter is unceasing and continuous between the 

 earth, the air, and the water on the one hand, and 

 all living organisms, animals, or plants, on the 

 other, we cannot help coming to the conclusion that 



