188 LIFE OX THE EARTH. 



grades and greater perfection as a physiological 

 problem; and to shew that in the buried worlds of 

 life this continual expansion of the general funda- 

 mental form, with a continual tendency to higher 

 and higher development, can be placed in evidence 

 as a matter of history. It is important to keep this 

 distinction in mind. 



DEVELOPMENT. 



The author of the Vestiges of Creation placed 

 before the English reader some sketches of the as- 

 pect of the animated world in successive geological 

 ages, and has proposed in relation to the vegetable 

 and animal kingdoms a full hypothesis of develop- 

 ment to fit the gradation from the simple Lichen and 

 Animalcule respectively up to the highest order of 

 Dicotyledonous trees and the Mammalia. He attri- 

 butes a great amount of change to the necessary 

 effect of variations in the physical conditions which 

 are influential on life: this change being progressive 

 from lower to higher grades, and unlimited except 

 by the range of physical conditions. 



'While the external forms of the various verte- 

 brate animals are so different, the whole are, after 

 all, variations of a fundamental plan, which can be 

 traced as a basis through the whole, the variations 

 being merely modifications of that plan to suit the 



