220 THE FROG CHAP. 



have obtained a footing, till an entirely new set of weeds 

 may take the place of those that first appeared. 



A struggle for existence goes on on all sides among 

 animals. To begin with, before there is any struggle 

 for existence in the strict sense, there is particularly in 

 animals which, like the frog, produce eggs in great 

 numbers annually a very great indiscriminate destruc- 

 tion of ova and young embryos. Only a few of them 

 reach maturity ; a large proportion are destroyed at one 

 stage or other, some failing to reach a spot favourable 

 for their further development, others becoming the food 

 of other animals. But such of the young as are less 

 adapted to escape the various dangers to be encountered, 

 and less fitted to procure the necessary food, are more 

 likely to be destroyed. This is one phase and the 

 most important, perhaps, of all of the struggle for 

 existence amongst animals. But there is also a struggle 

 for existence, not only between individual animals of the 

 same kind, but between animals of different kinds. 

 This struggle, in so far as it relates to the competition 

 for food and shelter, is more severe between nearly 

 related species ; for in such a case the food and the 

 favourable conditions required are the same, or nearly 

 so, in the two competitors. Again, a struggle for exist- 

 ence of a constant and severe kind also goes on between 

 carnivorous animals and the animals on which they 

 prey e.g., between the frog and the insects and worms 

 on which it feeds, and between the snake and the frog ; 

 a struggle in which the defensive qualities of the prey 

 such as swiftness, power of eluding observation, or 

 of resisting attack are opposed to the predatory powers 

 of the attacker. 



There can be little doubt that, in the long run, such 

 individuals will survive as are best fitted to cope with 



