366 THE WONDER OF LIFE 



mosquitos be not infected, then Yellow Jack is conquered. 

 As a matter of fact, the disease has been quite stamped out 

 in Havanna. 



It comes to this, then, that the great practical lesson of 

 Natural History is to recognize the complexity of inter- 

 relations, ' the wheels within wheels '. In a report of a 

 lecture by Mr. James Buckland, we read : ' The destruc- 

 tion of the white heron for its scapular plumes has robbed 

 half the world of a bird which is most useful to man. Its 

 loss to India and to China is most serious. It never touches 

 grain, but feeds solely near water and over damp ground, 

 the breeding-places of innumerable batrachians, small 

 crustaceans, and pestiferous insects, all of which directly 

 or indirectly injuriously affect crops in the neighbourhood. 

 The presence of the white heron in the rice-fields, for in- 

 stance, is distinctly beneficial to the farmer, and rice is 

 one of the most extensively grown crops of India and of 

 China.' 



In this connexion it may be useful to point out that 

 many eliminations consequent on Man's intrusion cannot 

 be directly brought home to him as the results of any 

 ruthlessness. Thus one of the most extraordinary of 

 recent disappearances is that of the Passenger Pigeon 

 (Ectopistes migratorius) which used to breed, within the 

 memory of living man, in huge numbers in the North 

 American forests. Wilson, the American ornithologist, 

 estimated a flock at 2,230 millions, and in 1912 there was 

 said to be only one individual left, a female bird, about 

 nineteen years old, belonging to the Zoological Society of 

 Cincinnati. It is difficult to believe that there are not 

 survivors in the woods, but persistent efforts to find them 

 have not been rewarded with any success. 



