CHAPTER II 

 FORMS OF PARASITISM 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 by the various terms used in the 

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

 mendation that they 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 term at hand. With such a conception the student 

 should be able to formulate 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 terms have been treated of in foregoing 

 introductory remarks, they are here included for more concise definition 

 and to make the list inclusive. 



Symbiosis is the more or less permanent 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 harm to the other. 



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



Mutualism is a form of symbiosis in which both symbionts are in 

 more or less measure benefited by the union. 



Comanensalism is that form of symbiosis in which but one symbiont 

 is benefited, while its co-symbiont is neither benefited nor harmed by 

 the union. 



Helotism is a form of symbiosis 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 symbiosis in which one symbiont, for pur- 

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

 its abode temporarily or permanently, upon or within the body of its 

 co-symbiont which is harmed by the union. The symbiont receiving 

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

 host. 



Phytoparasites are parasites which belong with the vegetable 

 kingdom. 



