V] OF UNDULATING MEMBRANES 431 



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 b. 



Moreover, this mode of formation has been actually witnessed 

 and described, though in a somewhat 

 exceptional case. The little flagellate 

 monad Herpetomonas is normally desti- 

 tute of an undulating membrane, but 

 possesses a single long terminal flagellum. 

 According to Prof. D. L. Mackinnon, the 

 cytoplasm in a certain stage of growth 

 becomes somewhat "sticky," a phrase 

 which we may in all probabihty 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 „ 



, ., . ^ ,, . . , , Fig. 143. ^er^e^omonas assuming 



tail (so to speak), giving a rounded or the undulatory membrane 



sometimes annular form to the organism, of a Trypanosome. After 

 such as has also been described in certain ^- ^' ^^a^^^^^non. 

 species or stages of Trypanosomes. But again, the long flagellum, 

 if it get bent backwards 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 pseudo-undnlsitmg membrane (Fig. 143). The move- 

 ments of this structure were so exactly those of a true undu- 

 lating membrane that it was difficult to beheve one was not deahn^ 

 with a small, blunt Trypanosome"*. This in short is a precise 



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

 Amer. Acad, of Arts and Sci. li, pp. 289-378, 1915. Also C. H. Martin and Muriel 

 Robertson, Q.J. M.S. lvii, pp. 53-81, 1912. 



t D. L. Mackinnon, Herpetomonads from the alimentary tract of certain dungflies, 

 Parasitology, iii, p. 268, 1910. 



