PART III — ARTHROPODS 



CHAPTER XIX 



INTRODUCTION TO ARTHROPODS 



To the average person it is astonishing to learn that the insects 

 and their allies, constituting the phylum Arthropoda, include 

 probably more than four times as many species as all other 

 animals combined. In this vast horde of animal forms are 

 included some species which are distinctly valuable to the human 

 race, such as bees, the silkworm, the thousands of insects (Dip- 

 tera and Hymenoptera) parasitically destructive to injurious 

 species and the predaceous beetles; a great number which are 

 indifferent as regards their economic importance serving, perhaps, 

 only to arouse admiration for their beauties or disgust for their 

 loathsomeness; and man}' which are of great importance as 

 crop pests or as annoyers of domestic stock or of man himself. 

 Only relatively very few, a mere handful, are injurious to man as 

 parasites or as disease carriers, but these few are of almost in- 

 calculable importance. As mere parasites the parasitic arthro- 

 pods are of minor importance, but it is in their capacitj'^ as inter- 

 mediate hosts of other parasites or as mechanical carriers of 

 disease germs that these animals have to be reckoned with as 

 among the foremost of human foes. Every arthropod, para- 

 sitic or otherwise, which habitually comes in direct or indirect 

 contact with man must be looked upon as a possible disease car- 

 rier. The role of arthropods in the dissemination of disease is a 

 matter about which practically nothing was known 35 or 40 

 years ago. A French physician. Dr. Beauperthuy, in 1853 was 

 one of the first to express a belief in the dissemination of various 

 diseases by mosquitoes and in the v6\o of the housefly in the 

 spread of pathogenic organisms. In 1879 Manson first proved 

 insects to be intermediate hosts of human parasites, in the case 

 of Filaria and the mosquito. Since that time many of the most 

 important human diseases have been shown not only to be trans- 



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