1G0 THE VOYAGE OF H.M.S. CHALLENGER. 



oral cavities, communicating with a dorsal process ; d, base of a dorsal 

 process directed outwards, the rest being cut off; e, small ambulacra! 

 cavity which does not communicate with any process ; I, nerve branches ; 

 m, larger nerve passing to the process ; n, ambulacral nerve stem. The 

 radial ambulacral vessel does not appear. 

 Fig. 2. View of the ambulacral cavities which belong to one of the ventral lateral 

 ambulacra, seen from the inner side of the body-wall ; most of the con- 

 nective tissue is removed, a, ventral lateral ambulacral vessel ; b, 

 longitudinal muscular band ; c, transversal muscular layer ; d, branch of 

 the ambulacral vessel passing to a pedicel ; e, openings into the pedicels, 

 visible through the thin layer of circular muscular fibres as darker spaces ; 

 f, branched ambulacral cavities belonging to the pedicels and lying within 

 the ventral perisoma ; g, parts of the same ambulacral cavities crossing the 

 radial ambulacral vessel and extending beyond it, thus lying within the 

 lateral interambulacra ; h, ambulacral cavity belonging to one of the 

 processes of the ventral lateral ambulacrum ; k, opening into this process, 

 visible through the thin circular muscular layer as a darker space. 



Orphnurgus asper, Thdel. 



„ 3. View of a portion of one of the ventral lateral ambulacra, seen from the 

 peritonea] cavity ; o, branched ambulacral cavity belonging to a pedicel 

 and enclosed within the ventral perisoma ; b, branched ambulacral vesicle 

 or " ampulla " communicating with one of the processes of the ventral 

 lateral ambulacrum and depending freely into the peritoneal cavity ; 

 c, branched ampulla-like prolongation of the ambulacral cavity just men- 

 tioned; d, longitudinal muscular band and radial ambulacral vessel. 



Oneirophanta mutdbilis, Theel. 



,, 4. Transverse section of one of the ventral lateral ambulacra and of the adjacent 

 body- wall, a, radial ambulacral vessel ; b, ambulacral cavity of a process ; 

 c, ambulacral cavity of a pedicel from the outer row ; d, ambulacral cavity 

 of a pedicel from the inner row ; e, cavities communicating with adjacent 

 processes or pedicels ; f, inner pedicel ; g, outer pedicel ; h, process. 



Achlyonice paradoxa, Theel. 



,, 5. View of the anterior part of the odd interambulacrum, seen from the inner 

 side. <x, ambulacral cavities of the dorsal processes ; b, longitudinal 

 muscular bands and ambulacral vessels ; x, the anterior part of the odd 

 interambulacrum. 



