446 FAMILY: TIIYPANOSOMID.E 



leading to forms which are remarkably broad (Fig. 150, 37). In some 

 cases, both these modifications occur, with the result that there arise the 

 very remarkable leaf-like trypanosomes which are seen particularly in 

 amphibia (Fig. 150, 37). 



In other cases increase in thickness as well as breadth occurs, 

 and solid ovoid forms arise which are again typically seen in frogs 

 (Fig. 150, 39, and 238). 



It must be remembered that in ordinary stained films of blood these 

 complicated forms are generally distorted to such an extent that their 

 actual shape is obscured. The true form of the body can only be satis- 

 factorily seen in the living condition or in specimens fixed without drying. 

 Furthermore, during life the trypanosome is constantly altering its shape 

 by contractions of its body, but in relaxation it returns to one or other of 

 the types indicated in the diagram (Fig. 150). 



The length of the body behind the kinetoplast is also subject to 

 variation. In some forms the kinetoplast is actually at the posterior 

 extremity, or very near it, as in T. vivax, T. congolense, and the meta- 

 cyclic or infective forms of T. lewisi in the flea (Fig. 197, 20-23). In other 

 trypanosomes this region of the body may be greatly prolonged, as in 

 certain forms of T. lewisi in the rat (Fig. 197, 1-3) and the trypanosomes 

 which occur in toads (Fig. 238). 



The shape of the posterior end of the body is of some diagnostic 

 importance, though it must not be forgotten that the extremity is subject 

 to changes brought about by contractions of the living cytoplasm. Some 

 trypanosomes, like T. lewisi and T. cruzi, have habitually a very sharply 

 pointed posterior end, while others like T. vivax and T. congolense, have 

 this extremity rounded (Plate V., p. 456). Many pathogenic trypano- 

 somes not infrequently have the posterior end sharply cut off or flattened. 

 The swollen condition of the posterior half of the body in T. vivax is highly 

 characteristic of this species (Fig. 231). 



The undulating membrane naturally has its attached border shorter 

 than the free one, so that it is thrown into folds. The degree of undulation 

 varies in dift'erent trypanosomes, and consequently the length of the 

 axoneme. The degree of undulation is usually judged by the appearance 

 of the axoneme. In T. lewisi, in the forms which occur late in the infection 

 of a rat, the attached flagellum is only slightly undulating, whereas in 

 T. gambiense it is much more so (Plate V. a and l, p. 456). In other 

 trypanosomes the degree of undulation may be still more marked. 



As already noted, the axoneme may terminate at the anterior extremity 

 of the body, as in T. congolense and the stumpy forms of T. brucei and 

 T. gambiense, or it may be extended as a flagellum (free flagellum) for a 

 varying distance, as in the majority of forms (Plate V., p. 456). 



