650 FAMILY: TRICHOMONADID^ 



spiral manner along the dorsal surface to the posterior end of the body. 

 The posteriorly directed axoneme is attached to the border of the mem- 

 brane, and may be continued beyond it posteriorly for a short distance as 

 a fiagellum. The extension beyond the membrane of a flagellum does not 

 appear to be a constant feature. In some cases it is exceedingly difficult 

 to detect such a flagellum, especially if it is a short one, as is usually the 

 case. Faust (1921) regards the axoneme as terminating at the end of the 

 membrane (Fig. 266, 1-3). The membrane is in constant motion, while 

 the anterior flagella are sweeping over the body, first on one side and then 

 on the other. The flagellate progresses in a jerky manner, revolving con- 

 tinuously on its longiti^dinal axis owing to the action of its membrane. 

 When observed for any length of time, many of the flagellates in a specimen 

 become degenerate. Various changes may take place, all of which may 

 lead to misconceptions as to the character of the organism. The axoneme 

 may become detached from the membrane and lash about, so that if the 

 other finer flagella are overlooked, as is easily done, the organism may be 

 regarded as having only one long thick flagellum. Such forms have 

 probably been mistaken for Cercomonas. The flagellate may lose its 

 membrane flagellum entirely, while the cytoplasm at the anterior part of 

 the body throws out quite suddenly a long finger-like pseudopodium, 

 which travels backwards and at the same time becomes shorter. When it 

 reaches the posterior end of the body it vanishes, while another one is 

 formed again at the anterior end. These finger-like pseudopodia pass 

 down the body regularly, and may be regarded as a series of high narrow 

 waves, resulting from uncontrolled action of the membrane which has been 

 deprived of its axoneme. The movements are so peculiar that Castellani 

 (1905) was misled into describing this form as a new amoeba {Entamoeba 

 undulans). The posterior end of the body may become swollen, so that 

 the flagellate appears to have a spherical mass attached to it by a narrow 

 neck. This mass of cytoplasm may be broken off. In normal individuals 

 it is only the tip of the axostyle that protrudes from the body, but 

 in many degenerating forms, possibly as a result of retraction of the 

 cytoplasm or actual separation of portions of it, a greater length of 

 axostyle is exposed. If the flagellates do not degenerate, they gradually 

 become rounded and perfectly quiescent. In this condition the membrane 

 with its attached axoneme passes round the circumference of the now 

 spherical body, while the axostyle and basal fibre are curved within it. 

 The anterior flagella may entirely disappear. It is these rounded flagel- 

 lates which are suspected of proceeding to encystment, but encysted stages 

 of T. hominis have not been seen. In T. cavicB of the guinea-pig, however, 

 it is the spherical forms of this type which become encysted, and this 

 appears to be true also of T. muris of mice. Prowazek (1904fl) and 



