172 Cells; or, Evolution. 



other conditions that involved a concurrent progress 

 I conditions f rom tne inferior living species to the 

 of the superior. Coming down from the Si- 



rrogress. i ur i a n age to the present, through 

 those epochs and periods which I had occasion 

 to sketch before (No. 31), there has been a more 

 comprehensive succession of phases in the life 

 of the world, than there is to-day between the 

 equator and the poles, though that range varies 

 in its climate from the tropical and subtropical 

 zones, through the temperate, subarctic, and arctic 

 regions. There was much more in the progress of 

 the world. 



193. Hence, thirdly, there was an arithmetic of 

 progress about it; though one far different from that 



which evolution would require. If ani- 

 its Antii- j species evolved from one another, we 



should begin with one, or with a small 

 number, and reach by successive stages of geomet- 

 rical progression the present ample quantity of nearly 

 150,000. Suppose we began with 10, in the Silurian; 

 and that amounted to 34 in the Devonian, and to 

 in in the Carboniferous, and 387 in the Permian: 

 then in the secondary formations, proceeding at 

 the same rate of geometrical progression, we should 

 have in the Triassic, Jurassic and Cretaceous, 1163, 

 3830, 12,614, respectively: in all the tertiary forma- 

 tions, let us take only one step further, and put it 

 down at 45,500 species; then, in the present, at the 

 same rate of progress -we should arrive at the actual 



