172 



THE NEMERTINI 



FAMILY 1. EUPOLIIDAE, Hubrechu 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; 



Fio. X. 



Transverse section of Cerebrat ulus marginatus, Rcnier (modified, after Burger), o, epidermis ; 

 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 Heterpnemertines ; 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, pro bosci dial 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, parastomodaeal 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. 



