DISTOMIDiE. 



25 



perivisceral cavity, soon to be followed by many others in 

 company. These cercarias 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 distuictive to enable us to refer them to a 

 particular species of Distoma. The older writers, overlooking the 

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

 flukes. In their early cercarial state, these larv^ invariably exhibit 



Fig. 6. — Sporocysts of Distoma militare {ScoUces, Van Ben.) in a more advanced condition ; the 

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

 developed into tailed cercarice. — 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 further 

 advanced in development. Here they are seen twisted and folded 

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

 ventral sucker (acetabulum), 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 



