Introduction to Animal Morphology. i6i 



auricular processes on the head ; Rhynchodesmus and Geo- 

 desmus are terrestrial ; Procotyla has a cephalic, and Bdel- 

 lura a caudal sucking disc. 



Order 2. Rhabdocoela. — Intestine a simple pouch ; pharynx 

 not protrusible in some ; usually one sex-opening ; testes 

 pouch-like ; many are freshwater, others marine. This 

 order includes five families : — i . Microstomidae — proctuchous ; 

 mouth small, round, terminal in Proporus (eyes none), and 

 Disorus (eyes six), sub-terminal in Vorticerus ; it is slit-like, 

 sub-terminal in Microstomum, terminal in Schizoprora. 

 2. Pharyngeidae — pharynx protrusible, somewhat urceolate, 

 cylindrical, or conical ; mouth terminal (Acmostomum), or 

 sub-terminal (Vortex) ; it may be a transverse (Stenostomum), 

 or a longitudinal slit (Derostomum) ; or central, with a cylin- 

 drical (Mesopharynx), or funnel-shaped pharynx (Chonosto- 

 mum), or post-central, with one (Monocelis), two (Diotis), 

 or no otolith (Opistomum). 3. Apharyngeidse — pharynx 

 not protrusible ; mouth circular, sub-terminal (Strongoylsto- 

 mum), or medio-ventral ; eyes two (Mesostomum), or none 

 (Typhloplana) ; or the mouth may be slit-like, transverse, 

 behind the otolith (Convoluta), or longitudinal, terminal 

 (Telostomum), or sub-terminal ; eyes two (Macrostomum).* 

 4. Rhynchoprobolidse — having a terminal proboscis, and a 

 sub-terminal (Prostomum), or central, round mouth (Rhyncho- 

 probolus). 5. Catenulidae — several individuals united in a 

 longitudinal stock by continuous budding; head distinct; 

 European and South African forms. 6. Dinophilidce — form 

 a link to the next order, as they have a body cavity in which 

 lies the proctuchous stomach. They also have a number of 

 girdles of long cilia. 



Order 3. Nemertidea {CErsted, Rhynchocoela, Schultze) — 

 long, worm-like, mostly marine, proctuchous, dioecious,f 

 proboscis-bearing:!: Turbellarians, with contractile, brittle, 

 sometimes transversely striped bodies (rudimental annula- 

 tion), and numerous dermal muciparous glands, with some- 

 times a fourth muscular lamina (of internal longitudinal fibres, 



* Yelk and germ-glands united; separate in Orthostominn. 



T Except Borlasia hermaphroditica. 



X Proboscis small in Prorhynchus and in Polia involuta. 



