1010 PARASITES OF PROTOZOA 



of these errors, but there are sometimes greater difficulties in the way 

 of correct interpretation than might be supposed. 



A large number of organisms symbiotic with Protozoa are Schizo- 

 mycetes or Phycomycetes. In the latter group, Chytridiales are especially 

 widespread, as parasites of both the cytoplasm and the nucleus. There 

 are in all the major groups of Protozoa species that are symbiotic with 

 other Protozoa. Some groups of these, such as the Metchnikovellidae 

 and endozoic Suctoria, are known only from hosts of this phylum. Only 

 a few Metazoa occur as parasites in Protozoa. Although the relative size 

 relationships are sometimes such as to make it possible, parasitization 

 by these higher forms is not less prevalent than might be expected, in 

 the light of the infrequency, in general, of intracellular parasitism by 

 Metazoa. 



Cyanellae, chlorellae, and xanthellae have not been included in this 

 account of symbionts of Protozoa. The last two types, at least, are 

 widespread in members of many free-living groups, the former in fresh- 

 water forms, the latter in marine species. Although inhabiting the 

 cytoplasm, the nutritive processes of these organisms are autotrophic; 

 and they are not necessarily dependent on the host. Their relationship 

 to their hosts is often cited as mutualistic, in one way or another. The 

 problem is in part the same as that of the relationship of similar endo- 

 symbionts to many invertebrate animals — a problem that has been re- 

 viewed by Buchner (1930). Pascher (1929) discussed the endosym- 

 biosis of blue-green algae in Pai/linella chromatophora and some other 

 Protozoa, as well as in algae. Lackey (1936) described "blue chromato- 

 phores" in Paidinella and a number of flagellates, although he failed 

 to recognize them as resembling Pascher's cyanellae. Goetsch and Scheur- 

 ing (1926) discussed the relationship of the alga Chlorella to proto- 

 zoan and some metazoan hosts. The work of Pringsheim (1928) and 

 others has sustained the thesis of mutualistic symbiosis between Chlorella 

 and Protozoa. Most of the xanthellae have been placed in the crypto- 

 monad genus Chrysidella. Hovasse (1923a) maintained on the basis 

 of nuclear characteristics that xanthellae are dinoflagellates. 



Epibiotic Schizomycetes 

 schizomycetes on mastigophora 



Bacteria attached to the surface, either by one end or applied full 

 length, occur on many flagellates. They have been known for some 



