BIOLOGY IN ITS WIDER ASPECTS 1279 



improvements in the state of the immense quantities of trawled fish 

 brought to market. 



Second, there are those animals captured not for the sake of food 

 furnished directly by their liesh, but for the sake of other products, 

 which are often not edible. Here are included baleen whales, 

 elephants, beavers, birds of fine plumage, crocodiles for leather and 

 turtles for combs, inedible fishes for glue and manure, oysters for 

 pearls, and beetles for blisters. In one of the halls of the Oceano- 

 graphical Museum at Monaco there is an almost startling exhibition 

 of the variety of uses to which man puts the spoils of the sea. 

 This utilisation goes on apace. 



Third, there is the short list of animals that man has more or less 

 domesticated because of their direct or indirect utility — such as 

 dog and horse, sheep and cattle, goats and reindeer, pigeons and 

 poultry, ostriches and pheasants, silk-moths and honey-bees. Here 

 the modern biologist has to advise in regard to the application of 

 genetics to the improvement of breeds. Already for animals, 

 as well as for plants, the applications of Mendelism have worked 

 wonders. 



Fourth, there are the animals that favour man's operations, like 

 the earthworms that have made the fertile soil and the flower- 

 visiting insects that secure cross-pollination. Here the main service 

 of the economic biologist is to disclose and appreciate the vital 

 linkages that bind living creatures into an intricate system. Success 

 in preserving the long-established Balance of Nature depends very 

 largely on a sound knowledge of inter-relations. Ignorant eliminations 

 and introductions have proved very costly. But now man is learning 

 to play a positive part in preserving the balance, e.g. by introducing 

 an Australian Ladybird beetle to counter the ravages of the Aus- 

 tralian Fluted Scale-insect in California, where it was destroying 

 the citrus trees. 



Fifth, there are man's animal enemies, reduced in modern times 

 both in numbers and size. Most of the beasts of prey have ceased 

 to be important, save as yet in India, where they not so long 

 ago were destroying some 20,000 lives annually, and where also 

 as seriously the poisonous serpent still bites man's heel. Of far 

 greater mischief, however, are man's parasites, such as hookworm 

 and bilharzia; and also the vehicles of parasites, such as the malaria- 

 carrying mosquito and the sleeping-sickness-carrying tsetse fly. 

 The biologist has here both achievements and remaining tasks in 

 unravelling life-histories and discovering checks. 



The sixth group is composed of animals which injure man indi- 

 rectly, by attacking organisms that are useful to him, notably his 

 animal stock and his crops. The list includes voles, wood-pigeons, 

 worm-parasites, locusts, cockchafers and cotton-weevils, wheat- 

 midges and warble-flies. It is part of the task of the economic 



