CYTOLOGY 335 



is a case in point, for in certain infections this precocious flagellum for- 

 mation may have taken place to such an extent that nearly every indi- 

 vidual has two flagella (Fig. 159). It was this appearance which led 

 Prowazek (1904) to regard this organism as a biflagellate, and to state 

 that the type species of the genus Herpetomonas necessarily possessed two 

 flagella. It was proved, however, by the work of Patton (19086), Porter 

 (19096), Mackinnon (1910), and the writer (1911a) that the forms with 

 two flagella were in reality dividing forms in which precocious flagellum 

 formation had taken place in anticipation of coming division of the 

 flagellate. 



Fran9a (1920ff) maintains that in H. muscarmn there is actually a 

 division of the kinetoplast, intracytoplasmic portion of the axoneme 

 (rhizoplast), and the flagellum, while in flagellates of the genus Lepto- 

 monas, after division of the kinetoplast, a new axoneme grows out from 

 the daughter blepharoplast to form a new rhizoplast and flagellum. It 

 appears to the writer that such a distinction cannot be drawn between 

 the genera Herpetomonas and Leptomonas. 



UNDULATING MEMBRANE.— As already explained, in the crithidia 

 and trypanosome forms the axoneme passes along the surface of the body 

 to its anterior end, where it may or may not be continued into a flagellum. 

 In the majority of crithidia and trypanosomes the line of attachment of 

 the axoneme is raised into a thin ridge, the undulating membrane, which 

 varies in length with the position of the kinetoplast. It is attached to 

 the convex edge of the curved, blade-like body of the flagellate. The free 

 border is longer than the attached one, hence it is thrown into folds. The 

 axoneme runs along the free border, and the constant undulating move- 

 ments of the membrane are probably the result of contractions of the 

 axoneme, though some observers believe that they are due to certain 

 myoneme fibres which they claim to have detected. The membrane 

 consists of little more than the periplast, while the axoneme runs in a 

 canal at its margin. When the axoneme leaves the body of the flagellate, 

 the periplast is continued as the sheath of the flagellum. In some trypano - 

 somes the undulating membrane is broad and well developed {Trypanosoma 

 rotatorium), while in others it is very narrow (T. congolense). On the other 

 hand, in the trypanosome stages which occur in the development of 

 purely insect flagellates (Herpetomonas), well-developed undulating mem- 

 branes may be present in some cases, while in others there is no definite 

 membrane, the axoneme merely passing along the surface of the body 

 (Fig. 150, 40-45). This condition is well seen in the trypanosome stages 

 of H. mirabilis (Fig. 172). 



