172 



THE NEMERTINI 



FAMILY 1. EUPOLIIDAE, Hubrecht. There are no lateral, horizontal, 

 cephalic fissures. Eupolia, Hubr. ; the head is sharply marked off 

 from the trunk, into which it can be retracted. Poliopsis, Joubin ; 

 with a dorsal and a ventral median cephalic furrow, and a circular 

 furrow between head and trunk. Valencinia, Quatref. ; head awl- 

 shaped ; rhynchostome ventral. FAMILY 2. LINEIDAE, M'Intosh. A 

 deep, horizontal fissure on each side of the head, into the hinder end of 

 which the cerebral organ opens. GROUP A. Amicrurae. Without a small, 

 filamentous tail. Linens, Sowerby ; unusually long, thread-like body; 



Transverse section of Cerebratulus marginatus, Renier (modified, after Burger) 

 b, connective tissue or cutis, into which the epidermal glands dip, and which is occupied by 

 the outer coat of longitudinal muscles, characteristic of the Heteronemertines ; c, circular coat ; 

 d, longitudinal coat of muscle ; e, lateral nerve stem ; /, outer ring of nerve fibres ; g, blood- 

 vessel passing from lateral trunk to the parastomodaeal plexus (h) ; i, stomodaeum ; j, dorsal 

 nerve; k, proboscidial sheath nerve; I, deep nerve ring; m, vessel of proboscis sheath; n,' 

 aperture of excretory organ ; o, excretory tube, receiving below one of the finer canals ; p, 

 lateral blood-vessel ; q, parastomodseal vessel ; r, proboscis ; s, proboscis sheath ; the rhyncho- 

 coel is unlettered ; t, dorsal blood-vessel ; v, parenchyma. 



head broad and spathulate. The animals cannot swim, but creep at the 

 bottom or on the surface of the water, and can coil into clumps and 

 balls. Euborlasia, Vaill. ; body short, thick ; contracts like a snail. 

 GROUP B. Micrurae. With a small filamentous tail. Micrura, Ehrenb. ; small, 

 thin worms, unable to swim, but creep, coil into balls, and are contractile. 

 Mouth small and circular. Cerebratulus, Renier ; broad, strong worms, roll- 

 ing up spirally and not coiling ; they swim well, with eel-like undulations. 

 The lateral margin of the body projects as a distinct ridge. Mouth 

 long and slit-like. Langia, Hubr. ; lateral margins curved upwards pro- 

 duce a deep dorsal groove ; the margins are folded and lobed. 



