they have been discharged after passing through the bile-ducts 

 and intestine of the host. The egg produces a ciliated embryo 

 (miracidium) with eye-spots, apparently reflecting the free-living 

 ancestral stage, but with a boring organ at the enterior end of the 

 body. The embryo enters a pond snail (Lymnaea truncatula, 

 Europe; L. humilis, North America), giving rise to sporocyst, 

 redia, and cercaria stages, asexual or multiplication phases 

 through which the permanent specialization is gradually attained 

 and the number of young greatly increased. The tailed cercariae 

 become encysted on blades of grass, from which position they reach 

 the stomach of the sheep. The organism is accountable for the 

 disease known as "liver-rot" which has destroyed vast numbers of 

 animals in Europe, notably France. 



Many species of "flukes" and "distoms", as the trematodes are 

 commonly called, are parasitic on the epithelial surfaces of the 

 digestive tube and its appendages, lungs, and urinogenital organs in 

 vertebrates, a few occurring in man. Fasciolopsis buski, the largest 

 species, is very like the liver-fluke of the sheep both in appearance 

 and development. It inhabits the small intestine of man and the 

 pig in China, India and other parts of the Orient. Paragonimus 

 westermani is a common lung parasite of China and Japan. Clon- 

 orchis sinensis, also Oriental, occurs in the liver ducts, producing 

 profound modifications of the liver substance. Schistosoma haema- 

 tobium and 5. japonicum are two remarkable blood-parasites of man 

 and mammals, the former widely distributed in Africa, the latter in 

 China, Japan and the Phillipines. 5. haematobium is unisexual, 

 the male, an organism of 12 to 14 mm. in length, having the body 

 greatly flattened and the sides rolled in ventrally so as to form 

 a tube. The female, much more slender and 20 mm. in length, is 

 found more or less completely enrolled in the tube formed by the 

 body of the male. The eggs appear in the urinary bladder. They 

 develop in the water into embryos, which require certain species of 

 water snails for further growth and reproduction. From the snail 

 cercariae escape into water through which they are transmitted to 

 man. The structure and history of the Japanese form are similar. 



Cestoda. Taenia solium is one of two chief species having the 

 adult stage in man, the other being T. saginata. They differ in 

 their intermediate hosts, that of the former being the pig, and of the 

 latter the ox. T. solium is about 3 m. in length in average cases, 

 and lives on the epithelial wall of the human intestine. The 

 rostellum has a doubtlet circlet of hooks. There are four muscular 

 suckers. Passing backwards from the head or scolex there is a 

 gradual differentiation of proglottides, and of the formed prog- 

 lottids every stage is discernible from the appearance of the gonads 



