THE BALANCE OF NATURE. 169 



ber of germs produced by a single individual is so 

 great, that if they all lived and reproduced their 

 kind at the same rate, in a very little while the 

 earth itself would be too small to hold them. 



Leuwenhoek has calculated that a single speci- 

 men of the domestic fly can produce seven hun- 

 dred and forty-six thousand four hundred and 

 ninety-six young in three months. 



According to Professor Owen, a single aphis, or 

 plant louse, in the tenth generation produces one 

 quintillion young. 



It has been calculated that if all the offspring 

 of a single edible oyster survived for but a com- 

 paratively few generations, the waters of such 

 shallow inlets of the ocean as the Chesapeake Bay 

 would be too small to hold them. 



In order to avoid this excessive multiplication of 

 the animal and plant life of the earth, and the 

 above are but a few of the numerous similar cases 

 that might be quoted, and thus preserve the bal- 

 ance of nature, which would be disturbed by such 

 inordinate multiplication of any one species, all 

 forms of animate creation have their natural enemies 

 provided by nature to hold them in check. Those 

 only continue to exist that are best fitted to exist 

 under the conditions by which they are surrounded. 



H 16 



