DISTOMIDiE. 



25 



perivisceral cavity, soon to be followed by many others in 

 company. These cercarise are, at first, shapeless, irregularly elon- 

 gated bodies, but after passing through a series of gradations they 

 ultimately assume a well-marked definite form, which, in many 

 cases, is sufficiently distinctive to enable us to refer them to a 

 particular species of Distoma. The older writers, overlooking the 

 fact of their being only larvae, described many of them as adult 

 flukes. In their early cercarial state, these larvae invariably exhibit 



Fia. 6. — Sporocysts of Distoma militare (Scolices, Van Ben.) in a more adranoed condition ; the 

 one (e) showing an early condition of the agamic progeny which in the other (f) has 

 developed into tailed cercarim. — Van Beneden. 



more or less conspicuously-developed tails, as may be seen in the 

 accompanying drawing (fig. 6 f ), where a number of them are 

 included in the cavity of the body of a sporocyst still farther 

 advanced in development. Here they are seen twisted and folded 

 in various attitudes, presenting, moreover, not only a cephalic and 

 ventral sucker (acetahulvm), but also a dark forked line within-^ 

 the latter constituting the first appearance of the digestive system 

 in accordance with the true distome type. At a still further stage, 

 and after their escape fi:-om the sporocyst, other structures come 

 into view until we get that well-known and perfected condition 



