168 THE VOYAGE OF H.M.S. CHALLENGER. 



Lcetmogone ivyville-thomsoni, Theel. 

 Fig. 7. View of an ambulacra! cavity of a dorsal process, seen from above ; most of 

 the integument is removed, a, ambulacrum ; b, ambulacral cavity ; d, 

 opening of the process into the ambulacra! cavity. The process itself is 

 cut off, only its basal portion being left. 



Kolga iiana, T/he'el. 

 ,, 8. Half-schematic transverse section of the odd ambulacrum ; a, connective 

 tissue of the integument ; c, longitudinal muscular band ; d, ambulacral 

 vessel ; n, radial nerve stem. 



Oneirophanta mutabilis, Thdel. 

 ,, 9. Half-schematic representation of a transverse section of a dorsal ambulacrum. 



a, inner layer of connective tissue of the integument ; b, transverse mus- 

 cular layer ; c, longitudinal muscular layer ; d, ambulacral vessel ; e, thick 

 hyaline membrane separating the ambulacral vessel from the radial nerve 

 cord ; f, cavities or branches which probably belong to the ambulacral 

 cavities of the dorsal processes ; g, epithelium lining the perivisceral 

 cavity ; n, radial nerve, cord. 



PLATE XLIII. 



Oneirophanta mutabilis, Theel. 

 Fig. 1. Longitudinal section of the head-part, a, main canals which combine the 

 water- vascular ring with the tentacles and the radial ambulacral vessels ; 



b, water- vascular ring ; c, circular pseudhsemal vessels ; d, ventral 

 pseudhaemal vessel ; k, calcareous ring ; m, elastic bands and threads ; n, 

 nerve ring ; o, anterior portion of the oral cavity ; p, posterior portion of 

 the oral cavity ; r, oesophagus ; s, intestine ; t, tentacular cavities ; v, 

 circular fold or valve ; x, Polian vesicle. 



Deima fastosum, Theel. 



„ 2. View of the perisoma round the anterior closed aperture of the body ; twice 

 the natural size, a, minute pajnlla? placed in a ring round the disk-like 

 portion of the perisoma ; b, aperture into the foremost portion of the 

 alimentary canal. 



,, 3. Side view of the foremost portion of the alimentary canal, with the left side 

 removed to show the position of the tentacles, a, the oral cavity ; b, 

 tentacles retracted ; c, anterior aperture of the alimentary canal ; d, 

 perisoma round the aperture ; e, layer of circular muscles ; f, fold. Twice 

 the natural size. 



