ANNULOSA. 



47 



Only the principal families of the Annelida are given above. The 

 genus Tomopteris is often considered as forming a special section of the 

 Polychsetous Annelides, to which the name of Gymnocopa (Grube) has 

 been given. The aberrant genus Polygordius is also sometimes referred 

 to a special division of the Annelida, characterised, among other things, 

 by the absence of seise and parapodia. 



(Quatrefages, Histoire Naturelle des Anneles marins et tfeau douce, Paris, 

 1863 ; M'Intosh, Article "Annelides," Encyclop. Britann., 1875 ; Ehlers, 

 Die Borstenwurmer, Leipzig, 1864 and 1868.) 



Pig. 41. Annelida. A, Head of Nereis incerta, viewed from beneath, and enlarged (after 

 Quatrefages) : d, The principal pair of chitinous jaws (the dark dots on the lobe behind these 

 are smaller denticles) ; pa', Internal pair of palpi ; pa, External or greater pair of palpi ; 1 1 t, 

 Tentacles. B, Foot-tubercle of Nereis, enlarged : no, Notopodium ; lie, Neuropodium ; c, 

 Dorsal cirrus ; c', Ventral cirrus; 666, Branchial filaments; a, Aciculse; ss, Sete attached 

 to the dorsal and ventral oars. 



CLASS III.-CKETOGNATHA (Arrow-worms). 



Genus Sagitta (fig. 42). 



(Krolm, Anatomisch-physiologische Beobachtungen uber die Sagitta bipunc- 

 tata, Hamburg, 1844 ; Gegenbaur, Ueber die Entivickeluny der Sagitta, 

 Halle, 1856 ; Busk, Species of Sagitta, Quart. Journ. Micros. Sci., 1856.) 



The genus Balanoglpssiis is an aberrant type, which is sometimes placed 

 in the neighbourhood of the Nemertean worms ; while others regard it 

 as the representative of a special section of the Anarthropoda, to which 

 the name of Enteropneusta is applied. 



