210 SLUGS, FLUKES, EELWORMS, ETC. 



germs which form within the rediss are exceedingly 

 like Tadpoles (see Fig. 155, p. 208) ; they are oval and 

 flat, and furnished with long slender tails more than 

 twice the length of the hody. 



These " Fluke Tadpoles," so to call them, are 

 technically called cercariae, meaning animals with 

 tails. On the escape of each cercaria from the redise 

 in which it was formed, it makes its way from the 

 body of the Snail into the water (if in a pond or ditch), 

 but shortly attaches itself to water plants or whatever 

 may be accessible. There it draws itself up into a 

 round ball, exudes a gummy secretion, wags its tail 

 violently, till at last the appendage, which has now 

 ceased to be useful, is thrown off, and the gummy sub- 

 stance hardening, the cercaria remains within the 

 covering as a little white spot on the plants, or on the 

 locality to which it has attached itself. 



It is mentioned, however, by Prof. Thomas that 

 ** if the infested Snails are crawling on the margin of 

 a ditch or over a damp field, the cercariae, on leaving 

 the Snail, at once proceed to form their envelopes or 

 cysts at the bottom of the grass, and so attach them- 

 selves to the stalks or leaves near the roots." 



The next step completes the circle of infestation. 

 When the grass, to which the white speck-like cysts 

 containing the young Liver Flukes adhere, is eaten by 

 the sheep, or other suitable hosts (as rabbits or hares, 

 &c.), the young Fluke comes out of the covering, and 

 passes to the liver of its host, increasing in bulk, 

 after being swallowed, from about the eightieth of an 

 inch, to the adult length of an inch or an inch and 

 a third. 



In the above note I have conveyed to the best of 

 my power a sufiicient abstract of the most important 

 points in Prof. Thomas's paper to give the ordinar}' 

 life-history of the Fluke, and in so doing I trust I 

 shall not be considered as appropriating unjustifiably, 

 the subject being one which can only be dealt with 

 by a specialist, Professor Thomas's paper being well 



