PLATYHELMINTHES 95 



B. Dendeocoelida. — Forms with fiattened iody and 

 hranched intestine. Testes and ovaries follicular. 

 Otocysts very rare. 



Tribe 1. Tricladida. — Body elongated. Intestine in three 

 main tranches, which diverge from a cylindrical retractile 

 proboscis. Testes and vitellarium follicular. Germa- 

 rium compact. Genital aperture single. 



Planaria and Dendrocoelum live in fresh water. 

 Gunda, which shows traces of metameric structure, and 

 Bdelloura, which is an ectoparasite of Limulv,s, are 

 marine. The leech -hke land planarians are chiefly 

 tropical. Bhynchodemus terrestris and Geodesmus 

 bilineatus are European. The former is found in 

 England amongst damp bark,, etc., in gardens and 

 woods. 



Tribe 2. Folycladida. — Body thin and broad. Numerous 

 branched intestinal caeca open into the stomach. Testes 

 and ovaries follicular. Genital apertures separate, tlie 

 male anterior to the female. A ventral sucker some- 

 times present. Marine. Thysanozoon, Yungia. '^ 



Class II. CESTODA. 



Chakacteeistics. — Endoparasitic Platyhelminthes, devoid of 

 mouth and alimentary canal. Organs of adhesion, in the 

 shape of chitinoid hooks or suckers, enable the parasite to 

 attach itself to its host. The nervous system is composed of 

 a cerebral ganglion and two lateral nerve cords. The coelom 

 is represented by irregular splits in the mesodermic paren- 

 chyma. The excretory system is of the Platyhelminthine 

 type, opening to the exterior by one or more pores, which are 

 sometimes furnished with a pulsating vesicle. The Cestoda 

 are hermaphrodite, the generative organs being usually 

 repeated many times. 

 One of the commonest Tapeworms found in man is Taenia 



saginata (mediocanellata) (Eig. 66), and it will be a convenient 



form to describe. 



The worm in question may attain a length of five or six 



yards, and may be composed of many hundred segments, often 



