438 
H. M. WOODCOCK AND G. LAPAGE. 
either of the crescents or of the ovals. Ovals can be 
recognised longer than the crescents and are probably more 
resistant (cf . below) ; bnt by the end of eight days the 
medium is so overrun by bacterial and fungal growths that 
nothing else can be made out. Dr. Ledingham, of the 
bacteriological department here, kindly had cultures of the 
parasites made for us on different media, and he also informed 
us that no development took place. 
Structure. — Selenomastix ruminantium presents 
some highly remarkable features in its morphology and 
minute structure. The usual and typical form is slightly 
crescentic (figs. 1, 5, 7, 18) ; in the larger individuals it is 
often very like a banana (figs. 25, 26). The parasite is never 
sickle or S-shaped ; and this is true however big and long 
the crescents may be. Further, in the vast majority of 
parasites, if not in all, the curve of the crescent lies in one 
plane, i. e. it is not spiral like that of a spirillum. Viewed 
in this plane the parasites have the appearance of consider- 
ably elongated ovals (figs. 8, 9). Nevertheless, now and 
again, but very rarely, one gets the impression of the 
slightest possible twist in the axis of the parasite ; thus in 
fig. 21 and to a less extent in Text-fig. E, there is an 
indication of one end of the body pointing rather in the 
opposite direction to the other. We have looked particularly 
for indications of a spiral character of the organism in life, and 
this appearance, which we have observed in only very few 
individuals, is the only one we have obtained. Moreover, we 
do not feel at all certain that this appearance corresponds to 
a permanent twist, however slight, in the body. For we 
have noticed, in watching certain individuals progressing 
forwards — sometimes, too, individuals in which no flagellum 
could be made out — that the hinder part of the body move« 
slightly to and fro, laterally, in a zig-zag manner, distinctly 
more so than does the front part, which is kept fairly steady; 
this may perhaps be caused by a slight voluntary twisting of 
the hinder end of the body, first in one sense and then in the 
opposite one, this movement serving to propel the body (cf. 
