THE HAEMOFLAGELLATES 209 



are fairly uniform in size (Fig. 7, A-D), the chief exceptions being 

 T. theileri (Fig. 33), which is much larger than the rest, varying 

 from 30 to 65 /A in length ; and T. nanum, which is correspondingly 

 minute, being only about 14 ^ long. The Piscine forms, on the 

 other hand, though possessing an equally great range, exhibit a 

 more regular gradation. Starting with relatively small types, like 

 T. remaki, var. parva, with a medium length of 30 p, parasites of all 

 sizes are to be met with up to T. granulosum (Fig. 8, K) and T. raiae 

 (Fig. 38, B), which are among the longest Trypanosomes known, 

 attaining a length of 80 /*. 



There is equally great diversity of appearance. Typically the 

 body is elongated and spindle-shaped ; it is generally more or less 

 curved or falciform, and tends to be slightly compressed laterally. 

 It may be, however, anything from extremely slender or vermiform 

 (Figs. 8, K; 34) to thick-set and stumpy (Figs. 8, A; 35). More- 

 over, apart from the fact that a full-grown adult, ready to divide, 

 is in many cases much broader than a young adult (cf. T. leivisi, 

 Fig. 20, B), considerable polymorphism also sometimes occurs (e.g. 

 T. rotatorium, Figs. 8, A, B; 37). Again, there can be little or no 

 doubt that, in some instances at any rate, sexual differentiation is 

 expressed by more or less pronounced differences in appearance. 

 In fact, from one reason and another, it is often practically impos- 

 sible to define any one type within hard and fast limits, either of 

 shape or size. 



In the biftagellate, Heteromastigine forms (Trypanoplasma and 

 Trypanophis), the anterior extremity of the body is that, of course, 

 from which spring the two flagella. With regard, however, to the 

 correct orientation in the uniflagellate Trypanosomes (the genus 

 Trypanosoma sens, lat.) considerable uncertainty exists. For the 

 present, 1 in order to avoid confusion, the two ends may be desig- 

 nated as flagellate or flagellar, and non-flagellate or aflagellar 

 respectively. On the whole, the flagellar extremity is fairly 

 uniform and nearly always more or less tapering ; but the non- 

 flagellate end presents great variation, being, as Laveran and 

 Mesnil point out, particularly plastic. On the one hand, it may 

 be blunt and even rounded off at the tip, as in certain individuals 

 of T. brucii (Fig. 7, B), T. equiperdum (Fig. 32, D), and in a Trypano- 

 some of Senegambian birds (Fig. 35) ; on the other hand, it may 

 be very long and attenuated, as in T. hannae (Fig. 7, G), occasionally 

 simulating a true flagellum to a remarkable degree, this being the 

 case in T. polyplectri. Between these two extremes all manner of 

 intermediate conditions are to be found. An instance which well 

 illustrates the great variability in one and the same form is seen in 



1 The whole question is so closely bound up with that of the phylogeay of the 

 group that its consideration is best deferred until the two can be discussed together 

 (se below, p. 246). 



14 



