CHEMICAL CEPTORS 99 



Thus Romanes mentions the extinction of white clover 

 in Suffolk as a result of the destruction of cats. The 

 plants were dependent for their fertilization upon the 

 humble bees, whose nests fell a prey to the rapidly 

 multiplying field mice which naturally profited by the 

 destruction of their enemies, the cats. A similar 

 disturbance was unexpectedly precipitated in Jamaica 

 by the introduction of the Indian mongoose to de- 

 stroy the cobra. In Jamaica, the mongoose, in addi- 

 tion to its natural prey, ate the eggs of the song birds. 

 The decrease in the number of the birds immediately 

 led to an increase of ticks, which preyed upon and de- 

 stroyed the cattle, and even the mongoose itself. In 

 some cases such reciprocal dependence of living crea- 

 tures upon each other for life is so close, that they may 

 be regarded as compound beings. Darwin cites many 

 instances of these simultaneously evolved organisms 

 among insectivorous plants. Other examples are the 

 crocodile bird which subsists upon pickings from the 

 teeth of the crocodile ; and the rhinoceros bird which 

 feeds upon insects buried in the hide of the rhinoceros, 

 while, like the crocodile bird, it pays for its board by 

 taking sudden flight at the approach of a stranger, 

 thus warning its host of the proximity of danger. 



If men and animals prey upon the vegetable world, 

 the vegetable world in turn preys upon the animal world 

 through the medium of microscopic life. The same 

 co-adaptations that obtain among macroscopic or- 

 ganisms obtain also between them and their micro- 

 scopic " parasites." And harmful as many of these 

 adaptations are for man, when the trial balance is 

 struck, they are, in the aggregate, of great benefit ta 



