226 THE FROG chap. 



existence in the strict sense, there is— particularly in animals 

 which, like the frog, produce eggs in great numbers annually 

 — a very great indiscriminate destruction 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 de- 

 velopment, 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 competi- 

 tion for food and shelter, is more severe between nearly 

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

 able conditions required are the same, or nearly so, in the 

 two competitors. Again, a struggle for existence of a con- 

 stant 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 the 

 conditions to which they are subject. According to 

 Darwin's theory of Natmal Selection, it is assumed that 

 such surviving individuals would transm.it their special 

 properties to their progeny, and there would thus be a 

 gradual approximation towards a perfect adaptation of the 



