VOL. LXXXV.] PHILOSOPHICAL TRANSACTIONS. 527 



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 1 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 quantity of white sedi- 

 ment ; while the globular ones are in general quite full and turgid *. This spe- 

 cies, 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 mus- 

 cular power of these animals. 



If the hydatid be carefully removed from the brain, immediately after the sheep 

 is killed, and put into warm water, it will soon begin to act with the different 

 parts of the body, exhibiting alternate contractions, and relaxations. These it 

 performs to a considerable extent, producing a brisk undulation of the fluid con- 

 tained in it ; the action is often continued for above half an hour, before the 

 animal dies ; and is exactly similar to the action of muscles in the more perfect 

 animals. This species of hydatid is very well known by the name taenia hyda- 

 tigena ; it varies considerably in its size ; one of those which I examined alive 

 was above 5 inches long, and nearly 3 inches broad at the broadest part, which 

 makes it Q inches in the circumference. The coats of the hydatid, in their re- 

 cent 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 re- 

 resemble paper made on a wire frame. This very minute structure is not met with 

 in membranes in general ; it may therefore be considered as the organization on 

 which their extensive motions depend. The coats of the different species of hy- 

 datids 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 muscular power, since there is no other mode of account- 

 ing 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 similar 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 taenia hydatigena, a structure evidently endowed with a si- 

 milar principle of action, the theories of muscular motion, which are founded on 

 the anatomical structure of a complex muscle, must be overturned. The sim- 



* This species of hydatid without a necfc is also met with in the brains of sheep, but is less turgid, 

 and less of a spbetical figure, than those commonly found in the liver. — Orig, 



