TRYPANOSOMES 71 



The undulating membrane is a lateral extension of the ectoplasm 

 or periplast, and is the main agent in locomotion. It is edged by the 

 flagellum, which forms a deeply stainable border to it. Within the 

 membrane substance, often arranged parallel with its edge, are a 

 number of fine contractile elements, the myonemes. These con- 

 tractile elements may also occur on the body of the trypanosome. 

 They are easily seen in some large trypanosomes, but are difficult of 

 demonstration in others, owing to their great fineness. 



Multiplication of trypanosomes in the blood is brought about by 

 binary longitudinal fission (fig. 26). Division is initiated by that of 

 the blepharoplast and nucleus. The division may be equal or sub- 

 equal, whereby differences in size of individuals partly arise. Multiple 



FIG. 27. Trypanosomalewisi. Multiplication rosettes. X 1,000. (After Laveran and Mesnil.) 



division by repeated binary fission, without complete separation of 

 the daughter forms, is known in some trypanosomes (e.g., T. lewisi), 

 and rosettes of parasites thereby are produced (fig. 27). 



The classification of trypanosomes is very difficult. Laveran 

 (191 1) 1 has suggested the examination of the relative length of the 

 flagellum as a diagnostic character, and so arranged these flagellates 

 in mammals in three groups. The first group included those trypano- 

 somes always having part of the flagellum free (e.g., T. evansi, 

 T. vivax) ; the second group comprised forms without a part of 



1 Ann. Inst. Pasteur, xxv, p. 497. 



