2 Trans. Acad. Sci. of St Louis. 



tion of the various kinds of parasitism, notwithstanding 

 the fact that the various symbiotic and other relation- 

 ships involved in the habits of parasites have received 

 the serious attention of parasitologists for years. It 

 might be mentioned, however, that a few years ago Stiles 

 compiled a list of the various kinds of parasites,^ as 

 recognized by different workers, and tabulated them ac- 

 cording to the basis upon which they were made. 



In regard to the third point, the significance of dis- 

 tribution according to host species, much more has been 

 done, but scarcely anything in the Acarina ; although here 

 there is perhaps, one of the very best groups in which 

 to study it. Professor Kellogg of Stanford University 

 has made an extensive study of the distribution accord- 

 ing to host species in the Mallophaga. 



The chief work upon this paper was done in the Ento- 

 mological Laboratory of Cornell University, and in its 

 preparation I have become indebted to several persons, 

 but especially to Professor Comstock, and to Dr. W. A. 

 Riley, who has made an extensive study of parasitism. 

 Professor V. L. Kellogg has also made suggestions which 

 have been especially valuable, since he has made a thor- 

 ough study of somewhat similar problems in the Mallo- 

 phaga, and Dr. R. H. Wolcott of the University of Ne- 

 braska has supplied me with valuable data in regard to the 

 habits of the "Water Mites." 



Definition of Paeasitism. 



But few terms exist in the biological literature of such 

 common usage as the term parasitism, yet few are so dif- 

 ficult of definition or so incapable of proper limitations. 

 Many attempts have been made to define parasitism ; but 

 as our knowledge has been extended we have been com- 

 pelled to recognize more and more its complexity; until 

 today perhaps no two naturalists could agree upon the 



' stiles, C. W. Parasitism. Proc. Ent. Soc. Wash. 3 : 6. 



