PLANARIAN WORMS. 
395 
PlAXARIAXS, OR TeRBELLARIA ApROCTA. 
Intestine without a posterior opening . — Hermaphrodite. 
Sect. A. — Hhdb docoda. Intestine a straight sac. Usually two eyes on 
the ganglia. Body generally of an elongate oval form. 
(a) With a muscular pharynx, usually exsertile. 
Genus 1. Prseganglionie region in the form of a conical muscular pro- 
boscis. Mouth circular. — Prostomem, Duges ( Rhynchopro - 
bolus, Acmostomum , Schmarda). 
„ 2. Prseganglionie region well developed, broad and blunt. Pharynx 
tub-shaped. — Vortex, Ehr. ( Derostomum of Duges). 
„ 3. Prseganglionie region not muscular, and reduced in size. Mouth 
circular, near the centre of the body. — Mesostohem, Duges 
( Strongylostomum Typhloplana of Oersted). 
„ 4. Prseganglionie region small. One eye. Body long and worm- 
like. Mouth central. (Marine.) — Moxocelis, Oerst. 
„ 5. Prseganglionie region reduced to a minimum. No eyes. Mouth 
towards the posterior end of the body. — Opistomem, 0. 
Schm. 
(0) A muscular pharynx is ivanting. 
,, 6. Mouth an oval opening, placed lengthwise near the fore end. 
Prseganglionie region small and flat. — Macrostomexi, Oerst. 
„ 7. As the last, but mouth a long slit. — Orthostomem, 0. Schm. 
„ 8. Mouth a cross slit. No eyes. (Marine.) — Coxvoleta, Oerst. 
„ 9. Prseganglionie region pinched off as a kind of head, carrying 
two tentacular processes. Mouth round, behind the eyes. — 
Vorticeros, 0. Schm. 
Sect. B. — Dendroccda. Intestine an arborescent or multiramose cavity. 
Eyes often numerous. Prseganglionie region broad and flat, often tentacular, 
forming a frontlet. Body flat, broad. 
(a) Digonopora. With double genital openings. All marine ; often bril- 
liantly coloured. 
(p) Monogonopora. With a single genital opening. Nearly all fresh- 
water or terrestrial. All with a large muscular pharynx. 
Genus 1. Body oblong, flat. Mouth subcentral. Frontlet* three-cornered, 
or with tentacula-like comers. Eyes two, with lenses. — 
Plaxaria ( Dendrocodum ). 
„ 2. Frontlet small. Eyes many. The rest as Planaria. — Polycelis, 
Ehr. (not De Quatrefages). 
„ 3. Body elongate and vermiform, often brilliantly coloured. 
Prseganglionie region (frontlet) large and broad, sometimes 
expanded as a hammer-head. Animals all terrestrial. — 
Geoplaxa. 
This synopsis of genera is no doubt in many ways imperfect, 
but I believe it gives a fair view of the principal divisions of the 
fresh-water forms. The Rhabdocoels are minute, and abound 
* This name is proposed by Professor Rolleston for the prsegangiionic 
region of Dendroccels. 
