CHAPTEE III 



The organisation of the Flatworms— The life-history of the Cestoda and 

 Trematoda — The development of the Marine Planaria — The influence of 

 Parasitism. 



THE THIRD RACE OR PHYLUM OF THE ANIMAL KINGDOM. 



PLATODES— FLATWORMS. 

 Systematic Review. 



Class I. Turbellaria. 



Free-living Platodes, with ciliated body epithelium. 



Order I. Polycladidse, Marine Planaria. 



Large Turbellaria with flat, leaf-sliaped body, vnth numerous ovaries and testes, 

 without vitellaria, mostly with 2 separate genital apertures. The intestine very 

 much branched, the branches anastomosing. 



Tribe 1. Cotylea. 

 With ventral sucker. Mouth and pharynx in the middle of the body or further 

 forward. Tentacles wanting or found at the anterior edge of the body. Anonyinus, 

 Thysanozoon, Ytmgia, Cycloporus, Stylostomum, EuryUpta, Prosthiostomum. 



Tribe 2. Acotylea. 

 Without sucker. Mouth and pharynx in the middle of the body or further back. 

 Tentacles wanting, or 2 dorsal neck - tentacles present. Planocsra, Leptoplana, 

 Trigonoporus, Cestoplana. 



Order II. Tricladidse (Fresh-water, Land, and Marine Planaria). 



The generally large body is long and flat. Mouth and tubular pharynx behind the 

 middle of the body. One common external genital aperture with 2 germaria and 

 numerous testes and vitellaria. The alimentary canal consists of an anterior unpaired 

 portion and of two lateral posterior limbs, which are again provided with side branches. 

 Planaria, Bendroccelum (in fresh water), Gcodeamus, Bipalium (on land), Gunda seg- 

 mentata (marine). 



Order III. Rhabdocoelidje. 



In fresh and salt water. Small forms. Intestine, when clearly distinguishable, 

 a straight tubular ctecum without or with very slightly pronounced lateral branches. 

 Body elongate, mostly cylindrical, more rarely flatly compressed. 



