CHAPTER XIX 



RELATIONSHIPS BETWEEN CERTAIN PROTOZOA 

 AND OTHER ANIMALS 



Harold Kirby, Jr,^ 



In the literature in which consideration is given to close rela- 

 tionships between organisms of different species the effort is often made 

 to group the associations discussed under definite categories. The cate- 

 gories are defined, and it is shown in what manner and to what extent 

 each separate association can be referred to its proper position. A reader 

 of this literature soon becomes sensible of the lack of agreement in al- 

 most every major particular. Unlike names are given to the categories, 

 definitions are dissimilar, there is difference of opinion or lack of exact 

 information on the nature of the relationship itself, and the impossibility 

 of making unequivocal distinctions is apparent in many instances. In 

 order to make an advance toward harmony of opinion, the bionomics 

 of many groups of living things must be taken into consideration. The 

 author must here confine his discussion to a statement of what he re- 

 gards as a satisfactory denomination of the types of relationship be- 

 tween Protozoa and other organisms, including other Protozoa, with 

 which they are intimately associated. 



At the outset, it is apparent that a comprehensive term is necessary 

 to designate all types of relationship between Protozoa and their hosts, 

 whether the Protozoa are epibiotic or endobiotic, whether they live at 

 the expense of their hosts or aid them in some way. Such a term would 

 be applicable also in the instances in which it is uncertain in what sub- 

 division an association belongs. The choice should be between two exist- 

 ing terms, parasitism and symbiosis, the latter of which has etymo- 

 logically exactly the meaning desired. Both words have been used in 

 the general sense. The word parasite, however, has by universal agree- 

 ment been used to designate an organism that lives at its host's expense. 



' Assistance rendered by personnel of Work Projects Administration, Official Project 

 number 65-1-08-113, Unit Cl, is acknowledged. 



