918 PROTOZOA AND OTHER ANIMALS 



fish, and reptiles; hypocomids (except the small genus Hypocoma) are 

 parasites of certain groups of molluscs; Astomata are mainly inhabitants 

 of annelids, to which most genera are limited; hypermastigote flagellates 

 occur only in termites and roaches; and certain groups of polymastigotes 

 are restricted to certain groups of termites (p. 923) . 



The problem of host-specificity is ordinarily approached from the 

 standpoint of the individual species; that is, the degree in which it is 

 limited to a particular host species. In strict host-specificity, the host is 

 rigorously determined; there is only one host for a species of symbiont. 

 As has been pointed out by Grasse (1935) and Wenrich (1935), strict 

 host-specificity is not a general phenomenon. Surveys of lists of species 

 and their hosts often bring out many instances in which there is only 

 one host for a species, for example, in the genera Giardia, Babesia, 

 Plasmodium, Haemoproteus, Leucocytozoon, and Eimeria. But such data 

 cannot be taken at face value, because the apparent strict host-specificity 

 may be based on insufficient search for the organism in other hosts, or 

 on a tendency of taxonomists to differentiate species on insufficient 

 grounds. More intense study in certain groups, as Trypanosoma and 

 Devescovininae in termites, has shown less rigorous limitation than at 

 first seemed to exist. More commonly, host-specificity is relative. The lim- 

 itation is to more or less related animals; and it depends, as Becker 

 (1933) and Wenrich (1935) have pointed out, on the characteristics 

 of the symbiotic environment, the opportunities for transmission, and 

 the evolutionary tendencies of the Protozoa. The phenomenon is of the 

 same nature as that of the geographical distribution of free-living or- 

 ganisms, though of course it is more complex. 



It is a commonplace that given animals have characteristic protozoan 

 faunules; this phenomenon is of particular interest when there are 

 faunules of particular types peculiar to major groups. In instances of 

 the highest development of this tendency, it can be predicted what types 

 of Protozoa will be found in unexamined hosts. One may be reasonably 

 certain of finding Opalinidae in anuran species, Ophryoscolecidae in 

 ruminants, and certain types of polymastigotes and hypermastigotes in 

 all termites other than Termitidae . 



Questions of distributional host relationships and host-specificity will 

 now be considered in greater detail in certain representative symbiotic 

 faunules. Two faunules have been selected for this purpose: ciliates of 



