TENTA, 149 
of reproduction. In some allied forms, however, the cyst 
or cystic stage produces several scolices, in which cases 
metagenesis is evident. 
Tenia solium is only found in man, and is chiefly 
dangerous owing to a liability of the cystic stage being also 
passed through in man, often in the brain. 
Tenia 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 :— 
Man. 
Tenia 
yer 
Scolex Proglotts 
IN 
Bladder Worm 
Cyst Embryos 
Pig. 
PHYLUM PLATYHELMINTHES. 
The Platyhelminthes, or flat-worms, form a well- 
defined group of the affinities of which little is known. 
The two types given, Déstomum and Tenia, represent the 
two “parasitic” classes of the phylum. 
1. TREMATODA.—The 7Zyematoda are all parasites, the 
Monogenea are mostly ectoparasites with one host, and the 
Digenea are endoparasites with two hosts. 
2. Cestopa.—The Cestoda illustrate enteric parasitism 
with entire loss of alimentary canal. They usually alternate 
between two hosts and show a cestoid and cystic stage. 
Tenia saginata is a common type found in the ox and man. 
It has no hooks and is larger than Tendéa solium. In these 
the cystic stage has only one head and is called a cysticercus, 
but in some, such as Zenia cenurus, alternating between the 
dog (cestoid) and sheep (cystic), the cystic stage has many 
heads and is called a Canurus. It produces “sheep-gid ” 
