400 WILLIAM NICOLL. 
The number of specimens occurring in one host is not very 
great, although Linton puts it atas many as one to two dozen. 
Olsson says he found many specimens, but it is not clear 
whether he means in each or altogether. Its frequency, 
however, is well established, and it is probably more 
often present than not, at any rate during the months of 
April to Aneust. 
The habitat is chiefly the middle reaches of the intestine, 
but | have found it, especially in the immature state, as far 
down as the rectum. The occurrence of young specimens at 
a lower level in the gut than the adults is characteristic of 
more than one species, and it is probable that the cysts 
traverse the whole length of the intestine before the cercariz 
are set free. Olsson records it from the rectum and stomach 
of the trout, also from the pyloric appendages of Thymallus 
vulgaris. Linton found it in the rectum of . Salmo 
my kiss. 
It is easily discoverable in the intestinal contents, being 
moderately large and of a pale but distinctly reddish colour. 
Olsson says the colour is white, and the difference may be due 
to the fact that my specimens were not seen till twenty-four 
hours after the death of the host, at which time the parasites 
were still alive, but very sluggish. ‘There is no very obvious 
reason, however, for believing that that would account for a 
change in colour. For the above reason little movement was 
observed in the parasite, but it was apparent that the neck or 
pre-acetabular part was much more mobile than the rest of 
the body. ‘The shape is elongated oblong, tapering towards 
either extremity, but more or less rounded according to the 
state of contraction; flattened dorso-ventrally. The con- 
tinuity of the anterior margin is interrupted by the projection 
of two or more of the circum-oral papillae. The surface of 
the body was thrown into irregular ruge, but that is 
commonly seen in Trematodes some time after the death of 
their host. The length of my mature specimens is fairly 
uniform—3-4 mm.; the immature specimens are in many 
cases less than 1 mm. Most observers are agreed in fixing 
