GRADES OP ORGANISATION. 297 



same great plan. "We may never know how they originate, 

 or why they exist, but we perceive the modes in which they 

 operate, and can determine the results of their harmonious 

 and incessant inter-actions. 



At the present day we know that the great regulators of 

 plants and animals are heat, light, and moisture. Some are 

 adapted to the warmer regions of the globe, some to the 

 temperate, and others, again, to the colder latitudes. Some 

 are fitted for life on the dry land, some for life in the 

 waters ; while others, again, are fitted for both, or even to 

 wing their way through the atmosphere. Some affect the 

 marsh, while others cling to the thirsty upland ; some re- 

 joice in the shallow waters of the shore, while others find 

 their fitting habitat only in the deeper ocean. Some are 

 restricted to specific centres of limited extent, and present 

 little variation in character, while others enjoy a wider 

 range, and break into numerous and often widely divergent 

 varieties. Such are the obvious conditions and distributions 

 of life now, and such we may be certain were the nature of 

 its conditions and dispersion sduring all previous periods. 

 Again, some plants are rooted independently in the soil, 

 while others find their subsistence on other plants, or even 

 in animals. A vast number of animals live on vegetables, 

 while others prey on the vegetable-feeders, and are fitted 

 alone for this mode of existence. The tooth to tear is as 

 necessary as the tooth to grind, the foot to seize as the foot 

 to run, the hand to climb as the hand to hold, and the limb 

 to fly as the limb to walk or the limb to swim. Such are 

 the arrangements by which the balance and harmonies of 

 life are now sustained, and such we may presume were the 

 methods by which its harmonies were secured in former 

 ages. Plant-feeder and flesh-feeder, life and death, repro- 

 duction and decay, are necessary concomitants in the great 

 biological scheme of creation. ~VVe perceive them operating 



