268 



THE FORMS OF CELLS 



[CH. 



Here we have three little organisms closely allied to the ordinary 

 Trypanosomes, of which one, Trichomastix (B), possesses four 

 flagella, and the other two. Trichomonas, apparently three only: 

 the two latter possess the frill, which is lacking in the first*. But 

 it is impossible to doubt that when the frill is present (as in A and 

 C), its outer edge is constituted by the apparently missing flagellum 

 {a), which has become attached to the body of the creature at the 

 point c, near its posterior end ; and all along its course, the super- 

 ficial protoplasm has been drawn out into a film, between the 

 flagellum {a) and the adjacent surface or edge of the body (6). 



Moreover, this mode of formation has been actually witnessed 

 and described, though in a somewhat exceptional case. The little 

 flagellate monad Herpetomonas is normally destitute of an undulat- 

 ing membrane, but possesses a single long terminal flagellum. 

 According to Dr D. L. Mackinnon, the cytoplasm in a certain stage 

 of growth becomes somewhat "sticky," a phrase which we may 

 in all probability interpret to mean that its surface tension is 



being reduced. For this stickiness is 

 shewn in two ways. In the first place, 

 the long body, in the course of its 

 various bending movements, is apt to 

 adhere head to tail (so to speak), giving 

 a rounded or sometimes annular form 

 to the organism, such as has also been 

 described in certain species or stages 

 of Trypanosomes. But again, the 

 long flagellum, if it get bent back- 

 wards upon the body, tends to adhere 

 to its surface. "Where the flagellum 

 was pretty long and active, its efforts 

 to continue movement under these 

 abnormal conditions resulted in the 

 gradual lifting up from the cytoplasm 

 of the body of a sort of fseudo- 

 undulating membrane (Fig. 92). The movements of this structure 

 were so exactly those of a true undulating membrane that it was 



* Cf. C. A. Kofoid and Olive Swezy, On Trichomonad Flagellates, etc. Pr. 

 Amer. Acad, of Arts and Sci. li, pp. 289-378, 1915. 



Fig. 92. Herpetomonas assuming 

 the undulatory membrane of' a 

 Trypanosome. (After D. L. 

 Mackinnon. ) 



