394 Coe — A Century of Zoology in Ameri 



tea. 



mated man's struggle against opposing forces would be 

 in large measure overcome. The results of recent work 

 in economic zoology, both in regard to the destruction of 

 enemies and protection of useful mammals, birds and 

 fishes, furnish a bright outlook for the future. 



Protozoology. — Partly as an experimental field for the 

 solution of general biological problems and partly 

 because of its practical applications the study of protozoa 

 has now developed into a special science. 



The results of the investigations of Calkins, "Woodruff, 

 Jennings and others have greatly supplemented our 

 understanding of the signification of such important 

 biological phenomena as reproduction, sexual differen- 

 tiation, conjugation, tropisms, and metabolism. 



From an economic standpoint the protozoa have 

 recently been shown to be of the greatest importance 

 because of the human and animal diseases for which they 

 are responsible. 



Parasitology. — The animal parasites of man, domesti- 

 cated animals and plants include numerous species of 

 protozoa, worms, and insects. Together with the bac- 

 teria and a few higher fungi they cause all communicable 

 diseases. When we consider that not only our health 

 but also our entire food supply is dependent upon the 

 elimination of these organisms we must admit that para- 

 sitology is the most important economically of all the 

 sciences. 



The reports of the investigations of Stiles and his 

 associates in the Hygienic Laboratory and of Ransom 

 and his staff in the Bureau of Animal Industry are widely 

 distributed by the federal government. The systematic 

 studies so ably begun by Joseph Leidy in the middle of 

 the last century have been continued by Ward, Linton, 

 Pratt, Curtis and others on the parasites of many groups 

 of animals. 



Economic Entomology. — Another extremely important 

 biological science, the practical applications of which are 

 second only to those of parasitology in importance, is 

 entomology. In the last few years economic entomology 

 has exceeded any of the other branches of biology in the 

 number of its investigators. The American Association 

 of Economic Entomologists has a membership of about 

 five hundred. The work of most of these is supported by 

 appropriations from the State and federal governments, 



