ON M US BURY CASTLE. 67 



reach its proper soil and position. Every 

 plant which fails, no matter how little, in any 

 one of these particulars, is utterly lost. Its 

 chance of producing posterity is wholly gone 

 from it. And the same is true of animals. 

 The butterfly, for example, must find food 

 as a caterpillar, and must escape the eyes of 

 birds ; it must hide itself away as a chrysalis ; 

 it must make itself proof against frosts and 

 rains ; it must hit upon sunny weather in its 

 full-fledged winged form ; it must find, woo, 

 charm, and secure its mate ; it must lay its 

 eggs on the proper plants, and in a safe posi- 

 tion. Thus every existing individual of every 

 species is the descendant of countless ances- 

 tors on each side, every one of whom must 

 necessarily have fulfilled all the complex 

 conditions of existence at every moment of 

 their lives. If they had not done so, it would 

 not be here en Evidence to answer for their 

 success. 



However, as all individuals are liable to 

 vary a little individually to be lighter or 



F 2 



