36 



The Rot in Sheep. 



the posterior of the two suckers is not terminal, but on the 

 inferior surface of the body, it constitutes the genus Distoma ; 

 three suctorious cavities characterise the genus Tristoma ; five 

 the genus Pentasioma ; and a greater number that called Poly- 



stoma." 



Form and Size. — The Distoma hepaticum varies in size in the 

 same animal, according to the age of the entozoon. Although 

 this is the case, it is a singular circumstance, hereafter to be 

 explained, that no distomata are found in long-existing cases of 

 rot so small as to warrant the belief that they had been hatched 

 from ova deposited within the biliary ducts. The form of the 

 entozoon is that of an oblong oval, flattened from side to side. 

 Its greatest breadth is anteriorly, immediately behind the central 

 sucker, from which point it gradually tapers to its caudal 

 extremity. When fully developed, the distoma will often attain 

 a length of an inch and a quarter, and a breadth of half an inch 

 at its widest part. Many of the smaller specimens, however, 

 do not bear the same proportion between their length and 

 breadth, being somewhat rounder in form. It is, however, to 

 be borne in mind, that on being removed alive from the biliary 

 ducts, the creatures are seen to contract themselves, so as to 

 appear very much smaller than they really are — a circumstance 

 which has often led to an incorrect conclusion with regard to 

 their real size, and consequently as to their age, and the length 

 of time they had been located within the ducts. 



Fig. 2. 

 Fully-developed Distomata. 



We here insert an engraving (fig* 2) of two distomata of ma- 

 tured growth, which will assist our exposition. One of them is 

 represented as exposing the ventral surface — that on the right — 

 and the other the back or dorsal surface. 



Colour. — The colour of the entozoon is found to vary, ac- 

 cording to the amount of bile which is contained within its 

 digestive system. If well filled with this fluid, the distoma has 

 a dark-brown or occasionally a brownish-black hue ; on the 

 contrary, if nearly empty, its colour is a yellowish-brown. Very 



