CHAPTEE XXVII 



ECONOMIC ZOOLOGY 



315. Uses of animals to man. Economic zoology treats 

 of the value of animals for the purposes of man. These 

 services are enormously varied, and in this chapter we can 

 give only a bare enumeration of some of the most conspicu- 

 ous lines of service, leaving the student to develop the 

 details. At the outset we may remember that most of the 

 species of animals have inhabited the earth longer than man 

 has, and that we have no right to suppose that the reason 

 for their creation was to render him some service. Thou- 

 sands and thousands of species can be of no possible use in 

 human affairs, and a few are related to man only through 

 their ability to inflict positive injury. Of harmful nature 

 are the insects with poison glands connected with the 

 mouth, many of those with stings, the snakes with venom 

 fangs, the poisonous Gila monster among lizards, some of 

 the great beasts of prey, and, perhaps most of all, the nox- 

 ious types of mosquitoes, who transfer to the human body 

 the germs of certain diseases, as malaria, yellow fever, and 

 filariasis. Other noxious animals are the vermin rats and 

 mice and the like which infest houses and may carry dis- 

 ease, the many forms of internal and external parasites, 

 intestinal worms, ticks, mites, and the like. Harmful in 

 other ways are the hordes of insects injurious to vegetation ; 

 and some mammals, as rabbits and gophers, are at times 

 extremely destructive to valuable plants. 



316. Domestic animals. The very earliest records of 

 man show that he trained those animals about him which 



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