on Muscular Motion. 
205 
quadruped and human subject. They vary in size, but those 
most commonly met with, are from one quarter of an inch to 
three quarters of an inch in diameter. 
Another species is of an oval form, with a long process, or 
neck, continued from the smallest end of the oval, at the ter- 
mination of which, by the assistance of magnifying glasses, is 
to be seen a kind of mouth ; but whether this is intended 
merely for the purpose of attachment, or to receive nourish- 
ment, is not easily determined. This species is found very 
commonly in the brain of sheep, and brings on a disease called 
by farmers the staggers. It is not peculiar to any one part of 
the brain, but is found in very different situations, sometimes 
in the anterior, at others in the posterior lobe. It is inclosed 
in a membranous cyst like the globular kind ; but differs from 
that species in one only being contained in the same cyst ; and 
the bag, or body of the animal, being less turgid, appearing 
to be about half filled with a fluid, in which is a small quan- 
tity of white sediment ; while the globular ones are in general 
quite full and turgid.* 
This species, from its containing only a small quantity of 
fluid, has a more extensive power of action on the bag, and is 
therefore best fitted for illustrating the muscular power of 
these animals. 
If the hydatid be carefully removed from the brain, imme- 
diately after the sheep is killed, and put into warm water, it 
will soon begin to act with the different parts of the body, ex- 
hibiting alternate contractions, and relaxations. These it per- 
forms to a considerable extent, producing a brisk undulation 
* The species of hydatid without a neck is also met with in the brains of sheep, 
/ but is less turgid, and less of a spherical figure, than those commonly found in the liver. 
