20 6 
Mr. Home's Lecture 
of the fluid contained in it ; the action is often continued for 
above half an hour, before the animal dies ; and is exactly simi- 
lar to the action of muscles in the more perfect animals. This 
species of hydatid, is very well known by the name tama by - 
datigeiiia; it varies considerably in its size; one of those which 
I examined alive, was above five inches long, and nearly three 
inches broad at the broadest part, which makes it nine inches 
in the circumference. 
The coats of the hydatid, in their recent state, exhibit no 
appearance of fibres, even when viewed in the microscope ; 
but when dried, and examined by glasses of a high magnifying 
power, they resemble paper made upon a wire frame. This 
very minute structure is not met with in membranes in ge- 
neral ; it may therefore be considered as the organization upon 
which their extensive motions depend. 
The coats of the different species of hydatids had all of them 
the same appearance in the microscope. 
The intestines, in some of the more delicately constructed 
animals, have a membranous appearance, similar to the bag of 
the hydatid, and we cannot doubt of their possessing a mus- 
cular power, since there is no other mode of accounting for 
the food being carried along the canal. The action of the 
intestines, not coming so immediately under our observation, 
makes them a less obvious illustration of this principle than 
the hydatid ; we may, however, consider their having a simi- 
lar structure, as a strong confirmation of it. 
If we compare the structure of muscles in the human body, 
with that of the membranous bag, which composes the taniar 
hydatigenia, a structure evidently endowed with a similar 
principle of action, the theories of muscular motion, which are 
