and ducts to the completion of the reproductive processes, ending 

 in the production of ripe proglottides containing myriads of fer- 

 tilized eggs and embryos. The embryos, enclosed by the egg 

 membrane, reach the alimentary canal of the pig and are set free. 

 The characteristic development takes place in the muscles where 

 the cysticercus is formed. The latter is transmitted to the 

 human intestine in uncooked or insufficiently cooked pork. The 

 cysticercus is of considerable size, being 6 to 20 mm. in length. 



The various genera of tapeworms are distinguished by differences 

 in the position of the genital pores. In Taenia these alternate 

 on the lateral margins of the proglottides. In Dipylidium they are 

 paired. In Diphyllobothrium they occupy the middle points of the 

 ventral surface. 



Echinococcus granulosus, a small tapeworm of the intestine of 

 the dog is significant on account of the large cysts produced in 

 man through the development of the cysticercus stage. The adult 

 form in the dog is a minute worm of 2.5 to 6 mm. in length, and 

 composed of a scolex and three segments. The cyst phase develops 

 in human beings, for the most part in the liver, and is distributed 

 among those who have habitual association with dogs, especially 

 Icelanders. The cysts contain innumerable scolices and reach a 

 gross size of 4 inches or even more in diameter. 



Hymenolepis nana is a slender tapeworm of 10 to 45 mm. in 

 length reported from various European countries and North and 

 South America. The parasites when present at all are present in 

 large numbers, and the host effects are correspondingly severe. 



Diphyllobothrium latum is a large tapeworm of 2 to 9 m. in 

 length, significant as a human parasite and on account of its aquatic 

 larval stage. The adult is found in the small intestine of dog, fox, 

 cat and man. The eggs develop in water, giving rise to spherical 

 ciliated embryos. These pass through a minute crustacean host, 

 but eventually reach the intestine of a fish, commonly the pike, 

 where they bore into the muscles and are found as small yellowish 

 encysted bodies known as plerocercoids. These are transmitted 

 to the human intestine through the medium of insufficiently 

 cooked infected fish. 



NEMATHELMINTHES. 



The Roundworms are cylindrical, unsegmented worms, hav- 

 ing a continuous body-cavity, the latter lacking typically a lin- 

 ing membrane. The surface is covered by a smooth cuticle. There 

 are three main divisions of the phylum, Nematoda, Gordiacea, 

 and Acanthocephala, the first-named division being the character- 



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