PLATHELMTNTHES 



I 



aracteristic appearance to tlie animal, serve for this pur- 

 (Fig. 89 F). These glands appear on the free Cercaria 

 as white opaque masses ; but when their contents have 

 passed out during the encjstment, the body of the young 

 worm becomes entirely transparent (Fig. 89 G). If the cyst, 

 together with the plant to which it is attached, is swallowed 

 by a sheep, the envelope is dissolved in its stomach ; the 

 young worm becomes free, and finally reaches the liver, 

 where, in the course of about six weeks, it develops into the 

 sexually mature Distomum hepaticum. 



The different Distomidae present great 

 differences as to the course of their de- 

 velopmental processes. The eggs from 

 which embryos are to emerge do not 

 always become free, but may be taken 

 up directly by the intermediate host, and 

 hatched out only when they have reached 

 its intestine (Distomum ovocaudatiim, ac- 

 cording to Leuckart). It is not neces- 

 sary that a sporocyst should be first 

 developed out of the embryo, and a Redia 

 out of it, as in Distomum, hepaticum, but 

 the sporocyst may become metamor- 

 phosed directly into a Redia. Sporocyst 

 and Redia in most cases beget directly 

 Cercariae. The sporocyst in Distomum 

 macrostomum and Gasterostomum fimhri- 

 atum is very aberrant in shape. In this 

 species it develops tubular processes, 

 which serve for the reception of the 

 Cercariae. The sporocyst of Distomum 

 m,acrostomum, known as Leucochloridium^ 

 which inhabits the liver and other organs 

 of Succinea amphibia, attains an extra- 

 ordinarily large size, for it sends out 

 processes into the antennae of the snail, 

 where, on account of their external re- 

 semblance to insect larvae, they are seen 

 I and eaten by birds (Zellee, Heckert). 

 I 



Fig. 90.— Cercaria Vil- 

 loti, Monticelli (after 



Vir.LOT). 



