G8 SLEEP. 



reitsoTi can actuallv be asslcrned for this remarkable 

 difference. 



Ill the world at large, night follows day with un- 

 erring regularity ; and night is a time when most 

 animals cannot readily perform their usual func- 

 tions, or exert their usual activities. To be sure, 

 there are some small eyeless creatures which swim 

 about in ponds and rivers, or in the depths of the 

 sea, to which night and day are all the same, and 

 yet in whose simple little organization the necessity 

 for sleep has never yet arisen. Furthermore, 

 there are some specially nocturnal animals, even 

 among the higher grades in the world of nature, 

 such as bats, owls, and badgers, whose peculiar 

 case must be considered later, as exhibiting the 

 true object of slee[) in a very special and topsy- 

 turvy manner. But taking the earth as a whole, 

 no fact is more conspicuous in its arrangement 

 than the fact that life generally is vivid and active 

 during the hours of daylight, while it is su])pressed 

 and dormant during the hours of night. To 

 creatures with eyes — excluding for the time being 

 a few obvious exceptions already noted — day is 

 of course the natural time for seeking food, for 

 building nests, or digging burrows, for performing 

 all the thousand and one varied acts of every-day 

 life, either of tlie h)wer world or of humanity 

 itself. The enormous majority of our dumb fel- 

 low-creatures walk or fly about freely in the open 



