THE HAEMOFLAGELLATES 



211 



have been recently infected (e.g. five or six days previously) this 

 extremity is enormously drawn out and tapering like a whip (Fig. 

 9). In such forms the flagellum is often very short. 



The two flagella, in Trypanoplasma and Trypanophis, are inserted 

 into the body close to the anterior end (Fig. 8, F, G). They are 

 quite separate from each other, and while one (that most anteriorly 

 situated) is entirely free and directed forwards, the other at once 

 turns backwards and is attached to the convex (dorsal) side of the 

 body for the greater part of its length. This latter flagellum 

 terminates in a shorter or longer free portion. 



The comparative degree of development of the two flagella in 

 different cases is worth pointing out, since it is very instructive in 

 a phylogenetic connection. Starting with Bodo lacertae, from a 

 type similar to which the biflagellate forms may be derived, both 

 flagella are of about equal total length, and the trailing one does 

 not reach the posterior limit of the body. In Trypanophis grobbeni 

 (Fig. 30) the posterior flagellum is more developed than the 

 anterior one, and attached to the side of the body, but its free 

 termination is very short. In Trypano- 

 plasma borreli the anterior flagellum and 

 the free portion of the posterior one are 

 of equal length. Lastly, in T. cyprini 

 the former is much shorter than the 

 latter, and shows signs of reduction. 

 From this condition to its disappearance 

 is but a small step. 



In all other Trypanosomes there is 

 only one flagellum, which is invariably 

 attached to the body in the same manner 

 as the posterior one of the biflagellate 

 forms. The point of origin of the 

 flagellum is generally near the non- 

 flagellate end, but may vary consider- 

 ably. Although there is usually a free 

 continuation of the flagellum, it may be 

 short or lacking (cf. Fig. 34). 



Along the dorsal side runs a char- 

 acteristic fin-like expansion of the body, the undulating membrane 

 This always begins proximally at the place where the attached 

 flagellum emerges from the body ; and its free edge is really con- 

 stituted by the latter, which forms a flagellar border, more or less 

 sinuous in outline. The membrane may be only narrow, and 

 chiefly discernible by its well-marked border (Figs. 7, A, G ; 8, c), 

 or it may be well developed and sometimes thrown into broad folds 

 or pleats (Figs. 7, F ; 8, A, B). Distally the membrane thins away 

 concurrently with the body. 



Fio. 9. 



T. lewisi, from a 

 rat five days after 

 inoculation to show 

 the remarkably long 

 aflagellarend. (From 

 an original drawing 

 kindly lent by Dr. 

 J. D. Thomson.) 



