WORMS. 241 



and another at hinder end of the triangle. The outer 

 surface of the body is covered with minute back- 

 wardly projecting spines, which present no hindrance 

 to the forward creeping of the body in the bile-ducts, 

 but make backward creeping or gliding impossible. 



Eggs Y^u °^ ^^ i^ch long, with a red shell possessing 

 a greenish sheen. They can only develop if they get 

 into water, and in wet years the 

 conditions are very favourable on 

 damp meadows, for under such 

 conditions the sheep-dung, with 

 the contained fluke eggs, is liable 

 to fall into pools of water. But 

 many of the eggs can develop in 

 years that are not so wet and on 

 dryer fields, as they may be 

 carried into a ditch by rain or on 

 the feet of the sheep. The larva 

 hatched from the egg of the liver- 

 fluke is j^ of an inch long, elon- 

 gated in shape, and swims about 

 freely in the water by means of a covering of cilia (Fig. 

 142, a). It soon finds its way into the lung cavity of a 

 small water snail (LymncBus trvmoatulus, Fig. 142, i), 

 loses its covering of cilia, and becomes broader, even 

 almost spheric)Bil. In the free-swimming larva there 

 are already to be found a collection of germinal cells 

 in the hinder part of the body ; later on, these cells re- 

 peatedly divide and form little heaps, which ultimately 

 become fresh individuals. The larva has, therefore, 

 passed into a second stage, and this is now known 

 as a sporocyst (Fig. 142, 6, c). The stage developed 

 asexually from the heap of germinal cells is dis- 

 tinguished from the sporocyst by a diflerently shaped 

 body and by the possession of a gut (with mouth, 

 pharynx, and intestine, but no anus), which is absent 

 in the latter. This stage is termed a " redia " (Fig. 

 142, d). From five to eight of them are usually 



B 



