498 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



to be derived from the areolar texture of the infested animal, 

 and of a middle or internal belonging to the parasite. 



Upon the surface, and in the substance of the external 

 tunic, the bloodvessels of the nerve can occasionally be seen, 

 and recognised by their contents. One or two vessels may 

 thus be observed coasting along the cyst, accompanied by 

 single nerve-tubes, or by bundles of these, or by a mass which 

 completely incloses and conceals the cyst. The second tunic 

 is a fine transparent membrane, wdiich lines the first, and has 

 in its turn its internal surface covered by an epithelial layer, 

 which is the third tunic of the cyst. The epithelia are flat, 

 irregular in shape, and somewhat opatpie. The third, or in- 

 ternal layer, formed by them, breaks up under the pressure of 

 the glass plates, so as to present rents or fissures passing in 

 various directions over it. 



The cyst, in addition to the worm, contains a small 

 quantity of fluid, in wdiich oil-like globules of various sizes 

 float. 



The worm is a Distoma, oblong, dilated in front, tapering 

 slightly towards its posterior extremity. The mouth, longi- 

 tudinally oval, and rather pointed posteriorly, is surrounded 

 by the usual suctorial disc. The acetabulum is situated at 

 the junction of the anterior and middle third of the animal, 

 and can be protruded from the surface of the body. 



On the anterior edge of the acetabulum a minute pore is 

 situated, and communicates wdth a sac, to be afterwards 

 described. 



At the posterior extremity of the animal another orifice is 

 placed, which forms the outlet of the large chyle-sac, and 

 apparently also of another sac, to be afterwards alluded to. 



The integument of the two anterior thirds of the body is 

 closely covered with short slightly-curved spines, directed 

 backwards. These spines are largest round the suctorial 

 mouth, and on the posterior part of the body are gradually 



