44 VERMES. 



Class I. Platyhelmia (Platyhelminthes). 

 Flat-Worms. 



Unsegmented worms, generally with flattened bodies. Body-cavity 

 imperfectly developed (mesoderm generally parenchymatous), and usually 

 an excretory system of longitudinal trunks with narrow branches. 

 Cerebral ganglia generally present, but never a ventral nerve-cord. 

 Mostly hermaphrodite. Many forms parasitic. 



Order 1. Turbellaria. Free-living flat- worms, with soft, ciliated, tricho- 

 cyst-bearing skin. Mouth and muscular pharynx, but no anus. Live 

 in water or damp places. 



Rhabdocoelida, small forms with intestine, when present, a simple 

 tube. Convoluta, no intestine. Micr stomum, fission, stiff tactile 

 hairs ; Vortex, Monotus. 



Dendroccelida, large forms, with branched intestine and follicular 

 testes. (a) Triclades (Monogonopora), elongated Dendrocceles with three 

 main divisions to intestine, and single genital opening. Land (Geodes- 

 mus in pot-earth ; Bipalium) and freshwater (Planaria torva, P. dioica ; 

 Dendroccelum lacteum) Planarians. Gunda (internal organs segment- 

 ally arranged), marine. (6) Polyclades (Digonopora), flattened leaf-like 

 marine Dendrocoales, with a central stomach and two genital openings. 

 Leptoplana tremellaris ; Thysanozoon (metamorphosis with Miiller's 

 larva); both marine. 



