208 H. M. WOODCOCK. 



flagellum becomes free, and is directed backwards like a tail. 

 A comparison of the degree of development of the two 

 flagella in different cases is very instructive in a phylogenetic 

 connection. 



In Trypanosoma there is only one flagellum, which is 

 invariably attached to the body in the manner characteristic 

 of the posterior flagellum of the biflagellate forms. The 

 point of insertion of the flagellum into the body is generally 

 near the non-flagellate end, but may vary considerably ; it is 

 in close relation with the position of the kinetonucleus, which 

 is discussed below (p, 216). Although there is generally a 

 free continuation of the flagellum, this may be short or 

 absent. It is very short in T. paddae and indifferent indi- 

 viduals of T. ziemanni, while in T. johnstoni (fig. 51) 

 and female forms of T. ziemauni (fig. o3a) the flagellum 

 ceases Avith the limit of the body. Laveran and Mesnil 

 (54) maintain that the same occurs in the case of T. dimor- 

 phon (fig. 49 i), but Dutton and Todd, who first described 

 this parasite (21), figure a distinct, free flagellum, sometimes 

 short, sometimes long (fig. 49ii). Further investigation is 

 necessary to decide this point. 



Along the dorsal side runs a characteristic fin-like expan- 

 sion of the body, the undulating membrane. This always 

 begins proximally at the place where the attached flagellum 

 emerges from the body ; hence, its distance from the non- 

 flagellate end is dependent upon the point of insertion of the 

 flagellum. The free edge of the membrane is more or less 

 sinuous in outline, which gives the structure, even when at 

 rest, a wavy appearance. The edge itself is really formed by 

 the attached flagellum, Distally the membrane thins away 

 concurrently with the body, and when it ceases the flagellum 

 becomes, with one or two exceptions, free. Probably, in fact, 

 in forms with a very tapering flagellar end, the last portion 

 of the body is constituted mainly or entirely by the undu- 

 lating membrane, Avhich has been drawn out in some such 

 manner as in the case of the anterior end of Trypano- 

 morpha. The membrane may be only slightly developed, 



