THE H^MOFLAGELLATES. 203 



varying, indeed, from 30 — 65 /x in length. The Piscine Try- 

 panosonies, on the other hand, though possessing an equally 

 great range, exhibit a much more regular gradation. Starting 

 with relatively small forms like T. remaki, var. parva, with 

 a medium length of 30 ju, parasites of all sizes are to be met 

 with up to T. granulosum (fig. 17 k) and T. rajas, which 

 are among the longest Trypanosomes known, attaining a 

 length of 80ju. 



There is equally great variation in respect of form. Typi- 

 cally, the body is elongated, more or less curved and spindle- 

 shaped, and tends to be slightly compressed laterally. It 

 may be, however, anything from extremely slender or vermi- 

 form, to thick-set and stumpy ; while, in some cases, the 

 pai-asites show little or no trace of the spindle-form, but 

 are squat and elliptical. Some authors are inclined to group 

 the parasites according to type of form ; the writer does not 

 think, however, that anything is to be gained by so doing. 

 It is very difficult to draw any hard and fast distinctions, 

 because of the individual variation. Apart from the fact 

 that a fully-grown adult, ready to divide, is, in many cases, 

 very much plumper than a young adult (cf. T. lewisi, fig. 

 27 A and b), there can be no doubt that considerable poly- 

 morphism ^ also sometimes occurs ; illustrations of this are 

 given below. Some of the chief variations in form, as found 

 in the different groups of Vertebrates, may now be discussed 

 a little more fully ; it will be seen that no particular type can 

 be said to be peculiar to a given class of hosts. 



On the whole the greatest uniformity is seen in the 

 Mammalian and Piscine Trypanosomes. Among the former 

 the typical fusiform shape prevails. The parasites may be 

 very slender (as in T. lewisi, fig. 16 A, and some forms of T. 

 gambiense, fig. 48 b), fairly so (as in the majority of cases, 

 fig. 16 B — d), or relatively thick-set (T. trans vaaliense, 

 fig. 50 c). The animals are usually either crescentic (fig. 16 b) 

 or sickle-like (fig. 16 d). Piscine Trypanosomes are nearly 

 always very elongated and often, relatively, quite as thin as, 

 ' This is, of course, quite apart from degeneration and involution forms. 



