xni, b, 5 Haughwout: Flagellated and Ciliated Protozoa 253 



and other small free-living amoebae, while Chlamydophrys ster- 

 corea closely resembles some of the free-living testate forms. 



The flagellates exhibit elaborate motile apparatus and, in many 

 cases, well-developed mouth parts for the ingestion of food. 



The ciliated parasites such as Balantidium, Nyctotherus, Dip- 

 lodinium, Ophryoscolex, and the like not only resemble free- 

 living forms in regard to their motile and food-getting organs, 

 but many of them are highly organized in other ways, through 

 the possession of neuromotor apparatus. Opalina seems to con- 

 stitute an exception to the rule. 



The absence in most parasitic forms of the contractile or 

 excretory vacuole, which is cited by many as a characteristic 

 of the parasitic protozoa, is not by any means necessarily, an 

 adaptation purely to a parasitic mode of life. It is an adapta- 

 tion, to be sure, but parasitism is not the only thing that de- 

 termines it. The marine species of protozoa for the most part 

 do not possess contractile vacuoles. The gradual transfer of 

 a marine species to a fresh-water environment will frequently 

 cause it to develop a contractile vacuole, which it will lose on 

 its return to salt water. So that the possession or absence of 

 this organelle seems to be governed largely by the osmotic 

 tension of the medium in which the organism finds itself. 



In other words, Are these forms to be considered as on the same 

 plane with the blood and obligatory tissue parasites as the try- 

 panosomes and coccidia? It would seem not. The intestinal 

 flagellated and ciliated protozoa of man, with the exception of 

 Lamblia, do not show evidences either of a high degree of adapta- 

 tion to a parasitic mode of life or evidences of structural degen- 

 eration as a result of parasitism. They have not found them- 

 selves. They are, in a measure, creatures of impulse subject to 

 the play of natural forces that are yet to be understood, respond- 

 ing to frequently changing stimuli by varied reactions that are 

 the despair of the physician and parasitologist alike. They have 

 yet to settle down and behave with the almost mathematical 

 regularity that we have grown to expect of their more conven- 

 tional brethren, such as the coccidia and trypanosomes. 



With the flagellates it appears that tissue parasitism is a 

 departure from the normal and with only lesser force would 

 this seem to apply to Balantidium and Entamoeba. It is per- 

 fectly clear that many of these parasites may live in the in- 

 testinal tract over long periods of time without causing trouble — 

 perhaps they may never cause trouble during the life of the 

 host. On the other hand, the day may come when some con- 



