XKW TYPE OP PI?,OTISTAN PARASITE. 
439 
Certes^ remarks^ above, tbougli there is never anything 
approaching an S-shape). 
The concavity of the crescent may be only very slight 
(figs. 1, 14, 16), or may be practically absent (Hgs. 2, 4, 11, 
12) ; small forms often appear thus. Individuals immediately 
resulting from division may be pyriform, differing from the 
ovals in having one end broader than the other (figs. 34, 35). 
We have not succeeded in finding an individual with both 
sides markedly convex, which at the same time possesses a 
dagellum ; in other words, we have not found a typical oval 
with a flagellum. The nearest approach to an oval shape is 
seen in figs. 4 and 11, and these individuals, though they 
still come in the category of» crescents (for one side is 
practically straight), nevertheless closely resemble certain 
ovals. When seen more or less in the plane of the curve, the 
body of a crescent can be distinguished from that of an oval 
by the fact that its ends are narrower and more tapering 
(figs. 8, 9). 
The flagellum is apparently always attached to the concave 
(or straight) side of the body, and in the majority of cases its 
point of insertion is about the middle of this side. But this 
point varies to a certain extent, particularly in the smaller 
forms, where the flagellum may arise much nearer to one end 
(tigs. 1, 3, also 18) ; we have never found it, however, 
actually terminal in origin. It is possible that this variation 
in the point of attachment of the flagellum may be partly 
dependent upon the process of division. The question of the 
orientation of the body is one of mucli difficulty. If the 
middle point of insertion of the flagellum represents approxi- 
mately the anterior end, then it is obvious that the body is 
greatly extended laterally. It is certain, however, that the 
parasite never progresses forwards in a direction at right 
angles to its long axis, i. e. broadside on, as it were. We 
have, in fact, no reason to suppose that this is the right view 
to take. The only clue to an orientation of the body is the 
indication we get from certain movements of progression of 
the parasites of an antero-posterior polarity ; in such cases 
