216 THE BOOK OF A NATURALIST 



That, for example, of the young cuckoo ejecting 

 its foster-brothers from the nest ; of slave-making 

 ants, and of the larvae of the Ichneumonidae feeding 

 on the live tissues of the caterpillars in whose bodies 

 they have been hatched. He said that it was not 

 perhaps a logical conclusion, but it seemed to him 

 more satisfactory to regard such things " not as 

 specially endowed or created instincts, but as small 

 consequences of one general law " the law of 

 variation and the survival of the fittest. 



