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LIFE, IN ITS LOWER FORMS. 
but if it pass into the carnivorous animal, it becomes 
Cestoid. 
Besides “ the staggers,” onr sheep-farmers are but too 
familiar with a disease that occasionally decimates their 
flocks, and which they term “ the rot.” It chiefly attacks 
the sheep when pastured in low wet meadows, and is 
caused by the excessive multiplication of a worm known 
as the Fluke ( Distoma hepaticuni), which infests the livers 
of these and other animals. It resembles a minute sole, 
about an inch long, with a sucking disk at each end, each 
of which was formerly supposed to include a mouth 
(whence the name “ double-mouth ;”) but the posterior 
one has been ascertained to bo a simple imperforate 
sucker. From the true mouth proceeds a single digestive 
canal, which soon divides into two main stems, one pass- 
ing down each side, and giving off secondary ramifications 
as they proceed, which branch like the fingers of a hand, 
or the twigs of a shrub, and thus spread over the whole 
body. As all the branches are ordinarily filled with dark 
bilious matter, they can be distinctly seen 'within the 
pellucid white flesh, forming two beautifully ramifying 
trees. 
Closely resembling the Fluke in their soft gelatinous 
flesh, their flattened form, and the ramification of their 
digestive canal, are the little worms called Planarice, that 
are found in great numbers on the submerged vegetation 
of our rivers and ponds. They are generally minute and 
black ; but we have some marine species on our coasts 
that are much larger, and are ornamentally tinted. 
“ These creatures, notwithstanding their apparent help- 
lessness, are found to live on worms or insect larvie ; 
