908 PROTOZOA AND OTHER ANIMALS 



tozoa, the flagellate recently discovered in pond water by Bishop (1935, 

 1936) in England, and by Lavier (1936c) in France is of much inter- 

 est. Bishop found it on four different occasions in the course of thirteen 

 months, in a small pond with thick, black mud and much decaying or- 

 ganic matter; and Lavier found it in samples from two separate places. 

 Many of its characteristics are those of a trichomonad and, as Lavier 

 pointed out, it seems to be the only free-living member of the Tricho- 

 monadidae. There is a slender axostyle, which often is extended into a 

 pointed, posterior projection of the cytosome, or itself projects from the 

 body. Sometimes the flagellate anchors itself to an object by the end of 

 the axostyle. There are three anterior flagella and a trailing flagellum 

 that usually adheres to the body, forming an undulating membrane, but 

 that sometimes, according to Lavier, is free. The nucleus is trichomonad 

 in position, structure, and division, and there is a well-defined para- 

 desmose. Its manner of progression, which diff^ers from that of other 

 free-living forms (Lavier), impressed Bishop with its similarity to the 

 movement of T richoinonas . Bishop (1935) wrote of it under the name 

 "Thichomonas" KeiUni n.sp. 



The flagellate differs from Tvitrkhomonas in the absence of a costa. 

 Lavier assigned it to the genus Eutrichomastix, which resembles Tri- 

 chomonas in all respects except the lack of the costa and undulating 

 membrane. Although it has been shown that the trailing flagellum of 

 Eutrichomastix may adhere to the body under certain conditions, the 

 usual presence of an undulating membrane in the pond flagellate differ- 

 entiates it from that genus. Neither Bishop nor Lavier made any men- 

 tion of the parabasal body or of an attempt to demonstrate it. If this 

 structure, so characteristic of Monocercomonas {Eutrichomastix') and 

 Trichomonas, is present, it would leave no doubt of the trichomonad 

 affinities of the organism; if absent, the flagellate would not show so 

 close a relationship to endozoic forms. Bishop (1939) proposed the new 

 genus Pseudotrichomonas for the organism. 



It is not possible to state that in this organism there is evidence of 

 the origin of trichomonads, which are widespread and evidently have 

 been adapted for a great period of time to endozoic existence. It may be 

 a survival of an ancestral type; on the other hand, there is the possibility, 

 which Bishop considered, that it might be a parasite of some cold- 

 blooded host that had survived and multiplied in the water. Rosenberg 



