652 TRYPANOSOMIASIS 



closely resemble trypanosomes in structure). This micronucleus 

 is often surrounded by an unstained halo, and in its neighbour- 

 hood, in certain species, a vacuole has been described as exist- 

 ing ; this has been considered by some to be analogous to the 

 contractile vacuole present in many protozoa, and its shape and 

 position have been made the basis of specific distinctions ; 

 Laveran, however, thinks it is an artefact. From the micro- 

 nucleus or from its neighbourhood there arises an important 

 structure in the trypanosome, the undulatory membrane. 

 This is of varying breadth, has a sharp undulating free margin, 

 and surmounts the protoplasm of the organism like a cock's 

 comb ; it narrows towards the anterior end where it becomes 

 the flagellum. Motion is chiefly effected by the undulations of 

 this membrane and of the flagellum. The latter is continuous 

 with the protoplasm of the body of the organism ; it stains 

 uniformly like it, except the free edge which has the reddish 

 hue of the chromatin. In different species of trypanosomes, 

 variations occur in shape, in length, in breadth, in the position 

 of the micronucleus (and therefore in the length of the undulat- 

 ing membrane), in the breadth of the membrane, in the length of 

 the free part of the flagellum, in the shape of the posterior end, 

 which is sometimes blunt, sometimes sharp, and in the presence 

 or absence of free chromatin granules in the protoplasm. It 

 may be said that the differentiation of species of trypanosomes 

 is often a task of great difficulty, as both morphological and 

 experimental study is necessary. 



Multiplication in the body fluids ordinarily occurs by longi- 

 tudinal, amitotic division (see Fig. 188). First of all, the micro- 

 nucleus divides, sometimes transversely, sometimes longitudin- 

 ally, then the macronucleus and undulating membrane, and lastly 

 the protoplasm. In some species the root of the flagellum only 

 divides, so that in the young trypanosomes the flagellum is short 

 and subsequently increases in length (Tr. lewisi) ; usually the 

 whole flagellum takes part in the general splitting of the 

 organism. 



In most cases in the circulating blood the parasites of a 

 species show differences in shape and size; usually there is a 

 form long and slender in both body and nucleus, the free part 

 of the flagellum being longer than the body and the protoplasm 

 free from granules. In another type the organism is broader, 

 with a larger and rounder nucleus and a blunter posterior 

 extremity; the undulating membrane is narrow and the free 

 part of the flagellum is shorter than the body, and the proto- 

 plasm contains granules. According to one view, the former is 



