TAENIA, 149 



of reproduction. In some allied forms, however, the cyst 

 or cystic stage produces several scolices, in which cases 

 metagenesis is evident. 



Tcenia solium is only found in man, and is chiefly 

 dangerous owing to a Hability of the cystic stage being also 

 passed through in man, often in the brain. 



Tcefiia is a striking instance of the effects of endoparasit- 

 ism, especially of the enteric type. (See Chapter IX.) 



The life-history may be illustrated diagrammatically : — 



PHYLUM PLATYHELMINTHES. 



The Platyhelminthes, or flat-worms, form a well- 

 defined group of the affinities of which little is known. 

 The two types given, Distomum and Tcenia^ represent the 

 two " parasitic " classes of the phylum. 



1. Trematoda. — The Trematoda are all parasites, the 

 Monogenea are mostly ectoparasites with one host, and the 

 Digenea are endoparasites with two hosts. 



2. Cestoda. — The Cestoda illustrate enteric parasitism 

 with entire loss of ahmentary canal. They usually alternate 

 between t wo ho sts and show"" a cestoid and cystic stage. 

 TcBnta saginata is a common type found iq the ox and man. 

 It has no hooks and is larger than Tcenia solium. In these 

 the cystic stage has only one head and is called a cysticercus^ 

 but in some, such as Tcenia camurus., alternating between the 

 dog (cestoid) and sheep (cystic), the cystic stage has many 

 heads and is called a Ccenurus. It produces '^ sheep-gid " 



