THE LIVER FLUKE —(Distoma hepaticum.) 
Of the intestinal worms that attack sheep, we notice as the most 
important the Silver Fluke (Distoma hepaticum). This species, be¬ 
longing to class ticolecida order Trematoda or “Suctorial worms” as 
given above, inhabits the gall bladder or ducts of the liver in sheep, 
and, as believed, causes the disease known as the “rot.” It derives 
its common name from its resemblance in form, to the flounder, of 
which “fluke” is a Scotch and Old English name. It is somewhat 
broad and tlattened, of an elongate ovate form, somewhat pointed at 
each end and is usually nearly an inch long, often much less, but 
occasionally more; its breadth at the widest part, which is towards 
the front, is about half its length. Its color is usually that of the 
organ in which it resides. It belongs to a very low type of beings; 
having neither eyes, true respiratory organs, heart, nor any other organ 
of special sense; the sexes are not even distinct, and the alimentary 
canal does not even pass through the body, but dividing and subdi¬ 
viding, permeates all parts of it, distributing the imbibed nourishment, 
which needs little or no assimilation to adapt it to use in forming 
the materials of the body. It is proper to state, however, that Youatt 
and other writers on sheep, distinctly affirm that flukes have eyes and 
even figure them. But what possible use they have for these organs, 
in the situation they occupy, it is impossible to say; and moreover, 
without nerves, of which there are but mere traces, these organs would 
be entirely useless, even if they were in the light. That they do 
possess eye-like spots at a certain stage of their life is true, but there 
is nothing to show that these are organs of sight or eyes in any true 
sense. What this author considers the heart and circulatory system, 
is probably the water vascular system found in these and all other 
animals belonging to this class, which is supposed by many to represent 
the respiratory system in the higher grades. He also supposes the 
eggs or spores, after being cast off, remain undeveloped until taken 
into the stomach by the sheep with its food, which, as will be seen, 
is an error. 
The species belonging to this order vary considerably in their trans¬ 
formations and habits, some passing through a cycle of six forms 
while others present only three or four. Some infest the liver or 
hepatic ducts of vertebrates, others infest the intestines of birds and 
batrachians, the gills of fishes, or paunch of ruminants; while others 
are found imbedded in the vitreous humour and lens of the eyes of 
certain fresh-water fishes such as the perch. 
The cycle of changes through which the liver fluke of the sheep 
passes has not been fully traced, but the life-history of Distoma mili- 
tare , another species of the same genus, which inhabits, the intestines 
of water birds has been nearly completely traced, and from it we 
may, with what we know of the life of the liver fluke, form a some¬ 
what correct idea of the history of its transformations. 
This species, as stated, in its perfect or mature state resides in the 
intestines of certain water birds. The ova or spore-like eggs which 
it produces are few, some eight or ten in number. From each egg 
issues a ciliated larva, which still retains something of the character 
of an egg although active, as there is an outer envelope in which 
there is the real animal, or in which it is developed, its history at 
