336 FAMILY: TRYPANOSOMIDiE 



METHOD OF REPRODUCTION. 



Reproduction takes place most usually by longitudinal fission (Fig. 160). 

 After division of the kinetoplast and nucleus, and formation of a new 

 flagellum, as described above, the cytoplasm divides by a fission com- 

 mencing at the anterior end between the flagella and extending backwards 

 till two flagellates result. The resulting organisms remain attached by 

 their posterior ends for some time till final separation takes place. The 

 newly-formed flagellates are usually equal in size, but quite frequently they 

 are unequal, so that a small form may be separated from one many times 

 its size. In these cases, though the cytoplasm of the two daughter 

 forms may differ in amount, the nuclei and kinetoplasts are equally divided. 

 In the crithidia and trypanosome forms the division is more complicated, 

 owing to the presence of the undulating membrane (Fig. 160, 9 i6). In 

 both these, after division of the blepharoplast has commenced, a new 

 axoneme begins to form from what will be the daughter blepharoplast. 

 This grows parallel to the original axoneme along the border of the un- 

 dulating membrane, and as the extremity of the new axoneme is closely 

 applied to the original one, the impression of longitudinal splitting may be 

 given. After the new axoneme has grown to some extent, the undulating 

 membrane commences to split from behind forwards and between the two 

 axonemes. The point up to which the membrane is split at any stage of 

 the process is always a little behind the end of the new axoneme, so that 

 beyond the point to which the membrane has split the new and old axonemes 

 still lie close together. The stage at which complete separation of the 

 axonemes takes place or the extent of division of the membrane depends 

 on the size of the daughter individual. If division into two equal flagellates 

 is taking place, then the process of new axoneme formation and splitting 

 of the membrane extends right up to the anterior end of the flagellate. If, 

 however, the division is into unequal flagellates, then there is a shorter 

 axoneme formed and a shorter membrane is split off. In either case there 

 results a flagellate with two axonemes, flagella, and undulating membranes, 

 and as division of the kinetoplast and nucleus will then be complete, with 

 two kinetoplasts and two nuclei. At this stage the body of the flagellate 

 divides, the fission commencing at the anterior end between the two flagella 

 and membranes. It extends backwards till two flagellates are formed, 

 each with a nucleus, kinetoplast, undulating membrane, and flagellum. 

 In the division of a trypanosome, therefore, the splitting of the membrane 

 and growth of the axoneme takes place from behind forwards, while 

 the body divides from before backwards (Fig. 160, 13-16). Division of 

 the non-flagellate leishmania forms also takes place after division of the 

 kinetoplast and nucleus. In these cases, in which the axoneme is still 



