STRUGGLE FOR EXISTENCE. 67 



We see this in the recent extension over parts of the United 

 States of one species of swallow, having caused the decrease 

 of another species. The recent increase of the missel-thrush 

 in parts of Scotland has caused the decrease of the song- 

 hrush. How frequently we hear of one species of rat taking 

 /he place of another species under the most different cli- 

 mates ! In Russia the small Asiatic cockroach has every- 

 where driven before it its great congener. In Australia the 

 imported hive-bee is rapidly exterminating the small, sting- 

 less native bee. One species of charlock has been known 

 to supplant another species ; and so in other cases. We 

 can dimly see why the competition should be most severe 

 between allied forms, which fill nearly the same place in the 

 economy of nature ; but probably in no one case could we pre- 

 cisely say why one species has been victorious over another 

 in the great battle of life. 



A corollary of the highest importance may be deduced 

 from the foregoing remarks, namely, that the structure of 

 every organic being is related, in the most essential yet 

 often hidden manner, to that of all the other organic beings, 

 with which it comes into competition for food or residence, 

 or from which it has to escape, or on which it preys. This 

 is obvious in the structure of the teeth and talons of the 

 tiger; and in that of the legs and claws of the parasite 

 which clings to the hair on the tiger's bod}^ But in the 

 beautifully plumed seed of the dandelion, and in the flattened 

 and fringed legs of the water-beetle, the relation seems at 

 first confined to the elements of air and water. Yet the 

 advantage of the plumed seeds no doubt stands in the closest 

 relation to the land being already thickly clothed with other 

 plants, so that the seeds may be widely distributed and fall 

 on unoccupied ground. In the water-beetle, the structure of 

 its legs, so well adapted for diving, allows it to compete with 

 other aquatic insects, to hunt for its own prey, and to escape 

 serving as prey to other animals. 



The store of nutriment laid up within the seeds of many 

 plants seems at first sight to have no sort of relation to other 

 plants. But from the strong growth of young plants pro- 

 duced from such seeds, as pease and beans, when sown in the 

 midst of long grass, it may be suspected that the chief use 

 of the nutriment in the seed is to favor the growth of the 

 seedlings, while struggling with other plants growing vigor- 

 ously all around. 



Look at a plant in the midst of its range ! Why does it 



