38 TERRESTRIAL ADAPTATIONS. 



has occasioned the physiological one, that the 

 structure of plants has been brought to be what it 

 is by the action of external causes, or that such 

 plants as could not accommodate themselves to 

 the existing day have perished, would be not only 

 an arbitrary and baseless assumption, but more- 

 over useless for the purposes of explanation which 

 it professes, as we have noticed of a similar sup- 

 position with respect to the annual cycle. How 

 came plants to have periodicity at all in those 

 functions which have a relation to light and dark- 

 ness ? This part of their constitution was suited 

 to organized things which were to flourish on the 

 earth, and it is accordingly bestowed on them ; it 

 was necessary for this end that the period should 

 be of a certain length ; it is of that length and no 

 other. Surely this looks like intentional provision. 

 Animals also have a period in their functions 

 and habits ; as in the habits of waking, sleeping, 

 eating, &c. and their well-being appears to de- 

 pend on the coincidence of this period with the 

 length of the natural day. We see that in the 

 day, as it now is, all animals find seasons for 

 taking food and repose, which agree perfectly 

 with their health and comfort. Some animals feed 

 during the day, as nearly all the ruminating 

 animals and land birds ; others feed only in the 

 twilight, as bats and owls, and are called crepus- 

 cular ; while many beasts of prey, aquatic birds, 

 and others, take their food during the night. 



