Development of the Livcr-Fluhe. 
453 
which, in the present state of the investigation, the evidence 
points most strongly as the bearers of the larval form of the 
liver-fluke, and which I desire to obtain from infected fields. 
With regard to the precautions to be taken against the liver- 
rot, I am able to say now still more definitely, that to prevent 
sheep from getting the disease, they must be kept away from all 
ditches, marshy places, &c., where such snails can be found. 
Addendum. 
Since the above report has been in type I have carried my 
researches further, and have been enabled to complete the cycle 
of forms which occur in the life-history of the liver-fluke. 
In a Limnceus truncatulus dissected on the thirty-first day 
after the first exposure to infection, I found that the rediae of the 
liver-fluke had much increased in size. The largest was 
1*12 mm. long, and '23 mm. broad across the middle of the 
body. The larger rediae contained nearly a score of germs in 
various stages of development. The smaller were still spherical ; 
the larger ones, situated more anteriorly, were of an irregular 
oval shape, with a smooth surface, and enclosed each in a loose 
and delicate pellicle. The largest germ was 'IIB mm. long by 
•073 broad. But there was no clear evidence as to the form 
these spores would assume. 
In another snail dissected at the beginning of the seventh 
week after infection, I found rediae containing cercariae, and 
although the latter were not quite perfectly mature, they were 
still far enough advanced to enable me to determine the 
character of the cercaria. I have mentioned above that 
Professor Leuckart found tail-less distome-larvae in a redia in 
L. truncatulus, and that, inferring simply from the anatomical 
character of the larvae, and notwithstanding that the form of 
the redia was unfavourable to such a conjecture, he considered 
himself entirely justified in assuming, until further results, that 
these belonged to Fasciola hepatica. But I have already shown 
that the characters of the redia and larvae furnished me with 
reasons for gravely doubting the correctness of this conjecture, 
and from my further researches I am now warranted in asserting 
that this tail-less form does not belong to the liver-fluke, for the 
true cercaria descended from the embryo of the fluke has a tail 
of considerable length. The body of the cercaria is about a 
quarter of a millimeter in length, the oral and ventral suckers 
are of nearly equal size (-05 — --OG mm.), the ventral sucker being 
situated just behind the middle of the body. The pharynx is 
quite distinct, and the digestive tract is simply forked, the two 
