STERELMINTHA. 



87 



Fig. 38. 



one class of animals to another so insensible, that the naturalist hesi- 

 tates with which to associate it. In the Distoma, in fact, notwith- 

 standing its intimate relationship with the Tsenioid Sterelmintha, 

 the first rudiments of nervous filaments are apparent, and we find 

 its whole organization approximating the nematoneurose type rather 

 than strictly exhibiting the simple structure common to the Acrita. 



The Distoma is commonly found in the liver and biliary ducts 

 of sheep, and other ruminants, deriving nourishment from the 

 fluids in which it is immersed. The body of the creature, 

 which is not quite an inch in length, is flattened, and resembles 

 in some degree a minute sole or flat-fish. At its anterior extre- 

 mity is a circular sucker or disc of attachment, by which it fastens 

 itself to the walls of the cavity in which it dwells, as well as by 

 means of a second sucker of similar form, placed upon the ventral 

 surface of the body. In the annexed diagram (Jig. 38) the 

 posterior sucker has been removed, 

 in order more distinctly to exhibit 

 the internal structure of the animal. 

 The name which this entozoon bears 

 seems to have been given to it from 

 a supposition that it possessed two 

 mouths, one in each sucker ; whereas 

 the anterior or terminal disc (a) only is 

 perforated, the other being merely an 

 instrument of adhesion. The ali- 

 mentary canal (b) takes its origin from 

 the mouth as a single tube, but soon 

 divides into two large branches, from 

 which ramifications arise which are 

 dispersed through the body, each ter- 

 minating in a blind clavate extre- 

 mity. These tubes, from being 



generally filled with dark bilious matter, are readily traced, even 

 without preparation ; or they may be injected with mercury intro- 

 duced through the mouth. 



Through the walls of the ventral surface of the body, two 

 nervous filaments (c) are discoverable, crossing over the root of 

 the anterior sucker or acetabulum, and, gradually diverging, may 

 be observed to run in a serpentine course towards the caudal 

 extremity, where they are lost : it would even seem that on either 

 side of the oesophagus there is a very slight ganglion, from which 



