154 EVOLUTION 



medicinal leech). Similarly, the struggle be- 

 tween species of the same.gmm w^TI r^n^rally 

 pyf*rA than b o tw^n thft fiprnV . nf 



This is illustrated by the 

 inevitable replacement of the black rat by 

 the brown, or of the large cockroach by the 

 small. The structure pf 



r>l ft]] ntllPrft With 



it. 



s: witness alike the teeth 

 and talons of the tiger, or the legs and 

 claws of the parasite clinging to his hair. 

 The albumen of a seedling favours its strug- 

 gle with plants already growing around it. 

 Darwin goes on to speak of two "canine 

 animals" struggling with each other in a 

 time of dearth; of mistletoe versus mistletoe 

 on the same branch; of mistletoe versus other 

 fruit-bearing plants; of a plant on the edge 

 of the desert in days of drought; and then 

 says, " In these several senses, which pass 

 into each other, I use, for convenience' sake, 

 the general term of Struggle for Existence." 

 NATURAL ^fifi^EcpiQN. How will this 

 struggle for existence act in regard to varia- 

 tion? Can the principle of selection, so po- 

 tent in the hands of man, apply under 

 Nature? Most efficiently; for, when we bear 

 in mind the constant occurpnrp of 

 the s 



