CASES OF ADAPTATION 141 



changes occurred, or when more marked diversities of soil and 

 vegetation, with exposure to more severe competition, were 

 brought about, those modifications of the environment ^vould 

 inevitably result in more marked and more varied adaptations 

 of form, structure, or habits, bringing about what we every- 

 where recognise as perfectly distinct species. 



In the present work I do not propose to go further into this 

 matter, which has been treated with sufficient detail and with 

 copious illustrations in my Darwinism and other works, as 

 well as in Darwin's classical volumes. The Origin of Species 

 and Animals, and Plants under Domestication. I will there- 

 fore now proceed to an account of some of those broader aspects 

 of adaptation in the organic world, which, so far as I am aware, 

 have hitherto received little attention. 



Some Aspects of Organic Adaptation 



Though such a very obvious fact, it is not always kept in 

 mind, that the entire animal world, in all its myriad manifes- 

 tations, from the worm in the soil to the elephant in the forest, 

 from the blind fishes of the ocean depths to the soaring sky- 

 lark, depends absolutely on the equally vast and varied vege- 

 table world for its very existence. It is also tolerably clear, 

 though not quite so conclusively proved, that it is on the over- 

 whelming variety of plant species, to which we have already 

 called attention, that the corresponding variety of animal spe- 

 cies, especially in the insect tribes, has been rendered possible. 



This will perhaps be better seen by a reference to one of 

 the best-known cases of general adaptation, which, because so 

 common and obvious, is often overlooked or misunderstood. 

 All lovers of a garden are apt to regard as an unmitigated evil 

 those swarms of insects which attack their plants in spring, and 

 in recurrent bad years become a serious nuisance and commit 

 widespread devastation. At one time the buds or leaves of 

 their fruit trees swarm with various kinds of caterpillars, while 

 at others even the oak trees are so denuded of their leaves as 

 to become an eyesore in the landscape. Many of our common 



