THE H^MOFLAGELLATES AND ALLIED FORMS 287 



from a given spot. Many trypanosomes, especi?lly the large stout forms, 

 are very sluggish in their movements, and show but little power of progression. 

 At the opposite extreme, in this respect, is the African parasite of cattle, well 

 named by Ziemann T. vivax, which, according to Bruce and his collaborators 

 (411, iii.), " dashes across the field of the microscope with such rapidity that 

 it is impossible to follow its movements, cyclone -like leaving a clear path, the 

 corpuscles in its track having been flung on either side. If it remains at the 

 same spot for a time, as it sometimes does, it has an appearance of great 

 energy and power, throwing the surrounding red blood-corpuscles about in 

 wild confusion." 



In the foregoing paragraphs the terms " anterior " and " posterior," as 

 applied to the trypanosome-body, have been used strictly with reference to 

 its mode of progression. It is pointed out below, in the comparison 

 with other types such as Trypano plasma and Crithidia, that the extremity 



Fio. 126. A, Trypanosoma tineas of the tench ; note the very broad undulating 

 membrane in this species; B, C, T. pence of the perch, slender and stout 

 forms. After Minohin, X 2,000. 



of the body which is anterior, in the strictly morphological sense, in one 

 species, may conceivably be posterior in another case. Hence some writers 

 avoid the use of the words " anterior " and " posterior," and substitute for 

 them ".flagellar " and " aflagellar " respectively, to denote the two poles of 

 the body. There is as yet, however, no concrete evidence for regarding the 

 flagellar extremity as morphologically posterior in any known species of 

 trypanosome. 



The undulating membrane is to be regarded as a fold of the periplast or 

 ectoplasm, into which the granular endoplasm may extend a short way in 

 some cases ; it arises from the body along a line which is sometimes spoken of 

 as " dorsal," an unnecessary refinement of terms. The free edge of the 

 membrane, with its marginal flagellum, can be shown by direct measurements 

 to exceed considerably in length that portion of the body to which it is at- 

 tached ; consequently its free edge is thrown into folds or pleats more or less 

 marked. In preparations, trypanosomes are seen to lie, speaking generally, 



