T 



THE ORIGIN AND SIGNIFICANCE OF PARASI- 

 TISM IN THE ACARINA.* 



Henry Ellsworth Ewinq. 



In the study of the origin and significance of parasi- 

 tism in the Acarina one is confronted by conditions ex- 

 tremely complex, on account of the great variety in the 

 forms met with and the complicated symbiotic relations 

 involved. In the preparation of the present paper the 

 writer made many and extended field observations of 

 these minute creatures, covering a period of several 

 years; and these have been supplemented by laboratory 

 experiments. 



In my treatment of the subject of parasitism in the 

 Acarina special attention will be given to three aspects 

 of the question: 



The causes leading to the origin of the parasitic habits, 

 and the subsequent development of these habits. 



The analysis and classification of the various aspects of 

 parasitism. 



The significance of distribution according to host spe- 

 cies. 



In regard to the first of these aspects, altogether too 

 little has been done by the way of scientific research, 

 and scarcely nothing in the Acarina. In this country 

 Professor H. Osborn has studied the origin and develop- 

 ment of the parasitic habit in epizoic insects. 



In regard to the second aspect it appears that as yet 

 we are without a very complete and analytical classifica- 



• Presented by title to The Academy of Science of St. Louis, Febru- 

 ary 19, 1912. Presented to the faculty of the Graduate School of Cor- 

 nell University for the degree of Doctor of Philosophy, June, 1911. 



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