4 Trans. Acad. Sci. of St. Louis. 



organisms have studied the aspects of parasitism and 

 helped settle many questions in regard to their nature, 

 significance and ecological relations. From the results of 

 these various workers and from my own observations, I 

 have been able to obtain a large amount of data in regard 

 to the various biological aspects presented in the dif- 

 ferent states of symbiosis which have been included un- 

 der the term parasitism. 



Although numerous and various kinds of symbiosis 

 have been considered under parasitism by others, for the 

 purposes of this paper the writer has decided to limit the 

 use of the term as follows : 



It must predicate the actual subsistence of one form 

 upon the bodily tissues or the physiological products of 

 the bodily tissues of another living organism. 



A host relationship will not be necessary in order to es- 

 tablish parasitism. 



The organism affected by the parasite is not necessarily 

 injured by the same. 



Limiting the term in this way, the following classifica- 

 tion of parasites can be made. This classification is in 

 a nature theoretical to the extent that in a few phases 

 of parasitism given, examples appear to be as yet want- 

 ing, but no doubt that more extended observation in the 

 plant and animal kingdom will reveal all or most of 

 them. 



A Classification of Parasites.'* 



Taking into account the nature and habits of the para- 

 sites themselves. 



Depending upon whether the parasite Is a plant or an animal. 

 Phytoparasites. 

 Zooparasites. 



*In giving this classification of the different kinds of parasites many 

 'Of the kinds are not designated by special names; the writer preferring 

 to define the kind of parasite given rather than inflict upon the general 

 student of biology any new technical terms, thus overloading a terrain- 

 'Ology already rather unwieldy. 



