THE HJIMOFLAGELLATES. 209 



narrow, and chiefly discernible by its tliickened flagellar 

 border, as in T. inopinatnm (fig. 17c), sometimes in T. 

 lewisi, and particularly in certain individuals of T. zie- 

 manni (fig. 32) and T. jolinstoni (fig. 51); in these cases 

 it is comparatively straight, and of abont equal narrowness 

 throughout. In most Mammalian Trypanosomes it is mode- 

 rately developed, and usually more or less curved and wavy. 

 Lastly, in T. rotatoriura (fig. 17 a and b), T. avium (fig. 

 lop),^ T. damonife (fig. 16 j), Trypanoplasma and most 

 Piscine Trypanosomes it is very well developed, and often 

 thrown into broad folds or pleats of varying number. 



Minute Structure. 



The body appears to be in all cases naked, without 

 distinct limiting membrane or cuticle. This is probably an 

 adaptation to the peculiar habitat, and would undoubtedly 

 facilitate nutrition, which, of course, takes place here solely 

 by osmosis. The occurrence of any differentiation of the peri- 

 pheral cytoplasm in the form of an ectoplasmic layer has only 

 seldom been noted. Most writers simply ignore the point ; 

 Laveran and Mesnil (56) say that they have not succeeded 

 in differentiating any ectoplasmic layer, either in T. lewisi 

 or in the other Trypanosomes they have investigated. 

 Wasielewsky and Senn (120),- however, observed such a lg,yer 

 in the case of T. lewisi, distinguished from the rest of the 



' According to Laveran and Mesnil there is a slight peculiarity in the 

 undulating membrane of T. avium, a well-marked line running in the 

 middle, parallel with its contour (fig. 16 F, l.s.) ; it does not appear to be 

 continuous, being interrupted at the narrow parts of the membrane. These 

 authors consider that it represents a fold. It rather recalls the strength- 

 ening filaments or ribs in the membrane of Trichomonas, and perhaps 

 serves a similar function. 



^ These authors use the botanical term " periplast " to denote this layer. 

 Not to enter here into a discussion of the various forms which Senn's 

 " periplast " assumes, it may be merely stated that, at any rate so far as 

 the Trypanosomes are concerned, the zoological designation of ectoplasm 

 undoubtedly best indicates its nature and character. 



