CHAPTER II 



FORMS OF PARASITIS:^I AND INFLUENCE UPON THE HOST 



Forms of Parasitism 



The student of parasitology will be greatly aided by an orderly and 

 progressive pursuit of the subject, an elementary' requisite to which is a 

 broad conception of what is implied b}' the various terms used in the 

 chapters which are to follow. Those below are not given with the recom- 

 mendation that the}' be memorized as to the exact wording set forth in 

 their definitions; more essential is such an understanding that examples 

 can readily be picked out, a typical illustration always being in mind for 

 application to the tenn at hand. With such a conception the student 

 should be able to fonnulate his own definitions, and this will be of more 

 advantage to him than accepting those set forth according to the con- 

 ceptions of another. 



Though some of the following tenns have been treated of in foregoing 

 introductory remarks, the}^ are here included for more concise definition 

 and to make the list inclusive. 



Symbiosis is the more or less pennanent living together of two plants, 

 two animals, or an animal and a plant, the union being in a measure 

 beneficial to both, or to one with or without hami to the other. 



Symbiont, — one of two organisms partaking of symbiotic relationship. 



Mutualism is a fonn of sjmibiosis in which both sjTubionts are in 

 more or less measure benefited by the union. 



Commensalism is that form of s^inbiosis in which but one sjinbiont 

 is benefited, while its co-s\anbiont is neither benefited nor harmed by 

 the union. 



Helotism is a form of s}^nbiosis in which one organism appears to 

 enslave the other, enforcing it to labor in its behalf. The term is applied 

 to such association in certain insects. 



Parasitism is that form of sjanbiosis in which one symbiont, for pur- 

 poses of procuring food, or food and shelter, visits briefly, or takes up 

 its abode temporarily or pennanently, upon or within the bodj' of its 

 co-s>inbiont which is harmed by the union. The sAinbiont receiving 

 the advantage is known as the parasite, to which the one injured is the 

 host. 



Phytoparasites are parasites which belong with the vegetable 

 kmgdom. 



