TWO-SUCKERED GROUP 



3441 



lias been computed half a million may be laid at a time pass into the intestine of 

 the sheep by way of the bile ducts, and thence make their way to the exterior. 

 Many of these eggs fall upon dry ground, where they 

 perish. Some however, in all probability, make their 

 way into water. When this has taken place, the egg, 

 after two or three weeks, gives birth to a free-swim- 

 ming, ciliated, conical embryo, provided with a double 

 eye and rudiments of an excretory system. By 

 means of its cilia, this embryo swims rapidly about in 

 search of a particular species of pond snail. If it fails 

 in its search, it perishes in about eight or ten hours; 

 but, if successful, it proceeds to bore its way into the 

 soft tissues of the mollusk. As soon as it has effected 

 an entrance, it loses its cilia and turns into an oval 

 sac, the sporocyst. The latter may multiply by fission, 

 but in any case, in its interior, another organism, called 

 after Redi, its discoverer, Redia, arises. This bores 

 its way out of the sporocyst, which closing up again 

 forms another; but if too many are developed they 



may cause the death of the snail. The Redia is cylindrical in shape, and has a dis- 

 tinct mouth and stomach, and in the hinder half of its body there is a pair of 



DEVELOPMENT OF Distomum 

 echinatum. 



LARVAL FORM OF LIVER FLUKE (magnified). 



bud-like processes, serving as rudimentary feet. The larva in this stage takes up 

 its abode in the liver of the snail, where, in turn, it proceeds to propagate. Its off- 

 spring may be a Redia like itself, but more often it has a different form, and has 

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