TURBELLARIA. 6 



papillae ; often very contractile and polymorphous, and some break- 

 ing up voluntarily into pieces. Head continuous with the body, or, 

 rarely, imperfectly defined, either without tentacula or with two 

 frontal or dorsal ones prolonged from the surface. Mouth either 

 terminal or ventral, and in the latter case situated in the anterior 

 third, or near the centre, or towards the tail ; often furnished with a 

 protrusile proboscis. Intestine dendritically branched or undivided, 

 with or without an anus. — Zoophagous, but some appear to feed 

 occasionally at least on decaying plants. Oviparous or viviparous, 

 very rarely multiplied by spontaneous division. There are no suckers 

 or discs, and progression is made by gliding or by natation. They 

 are never internal parasites, but tenant fresh and salt water, and are 

 found sometimes in moist places. The skin is very rarely iridescent, 

 and there is no phosphorescent species. 



The British genera may be classified in the following manner : — 



Suborder I. Planartea. 

 The body parenchymatous, flat or flattened, usually only a little 

 longer than broad, acephalous, with or without eyes on the dorsum 

 in front : mouth a simple pore, often the aperture to a protrusile 

 proboscis : anus none : genital pore posterior to the oral. 



* Intestine dendritically branched. 

 Family I. PL ANOCERID^. Flat : the mouth nearly in the centre 

 of the ventral surface, and furnished with a short proboscis cre- 

 nated or lobed at the orifice. 



1 . Leptoplana. Multocular, the eyes clustered : no tentacula. 



2. Eurylepta. Multocular, the eyes clustered: two frontal tenta- 



cula. 



3. Planocera. Multocular or eyeless : two dorsal tentacula. 



Family II. PLANARIADJE. Flattish: the mouth inferior, sub- 

 central, with a long cylindrical proboscis plain at the orifice. 



4. Polycelis. Eyes many, in a marginal series. 



5. Planaria. Eyes two, dorsal, and paired. 



** Intestine an undivided tube. 

 Family III. DALYELLID-ffi. Mouth terminal or subterminal, 

 eproboscidean. 



t Eyeless. 



9. Opistomum. Body elongate : mouth terminal. 



10. Typhloplana. Body linear-oblong : mouth ventral, subcentral. 



1 1 . Convoluta. Body involute. 



b2 



