230 On the Development of Antedon rosaceus. [Jan. 20, 



canal, containing a portion of the axial prolongation h. The middle part 

 of this canal communicates on either side with the interspace-system formed 

 by the infolding of the double wall of the alimentary canal ; and at I is seen 

 in transverse section, opening into the summit of the axial canal, one of the 

 radial subtentacular canals of the ventral disk. On the other side of the 

 mouth are seen two of the brachial subtentacular canals, one of them trans- 

 versely divided at i, and the other obliquely divided at k, about to coalesce 

 into a radial canal which passes round the oesophagus to open into the 

 axial canal. — This section has not laid open the quinquelocular organ in 

 the centro-dorsal basin ; but from its lower or dorsal margin several small 

 cords, I, are seen to pass off to enter the dorsal cirrhi. 



Fig. 3. Vertical Section of the Calyx, through a different plane from the preceding : — 

 a, b, c, d, e,/as in the last figure ; g, quinquelocular organ ; h, lower part of 

 the axial prolongation, springing from the central axis of the quinquelocular 

 organ, and passing behind one of the extensions of the glandular reduplica- 

 tion, to reappear above it at h', proceeding to the circular lip seen in 

 section at i; at k is shown the mass of connective tissue with its inter- 

 space-system lying between the duplications of the intestinal wall that form 

 the columella ; I, m, two of the axial (nerve ?) cords proceeding to the rays 

 from the upper or ventral margin of the quinquelocular organ. 



Fig. 4. Transverse Section of the Quinquelocular organ, viewed from its upper or ven- 

 tral aspect : — a, central axis formed by a prolongation of the axis of the 

 Crinoidal stem ; b, b, dissepiments forming five ventricular cavities; c, c, one 

 of the axial verticils sending off cords that seem to pass through the peri- 

 pheral wall to proceed to the dorsal cirrhi ; d, d, apertures by which the five 

 ventricular cavities communicate with the perivisceral space. 



Fig. 5. Vertical Section of the Quinquelocular organ, showing the division of its upper 

 or ventral portion b into chambers, and the occupation of its lower or 

 dorsal portion a by a succession of axial verticils giving off cords to the 

 cirrhi. 



Plate 9. 



Fig. 6. Transverse Section of decalcified Arm : — a, a, organic basis of calcareous seg- 

 ment ; b, solid axial (nerve ?) cord proceeding from quinquelocular organ ; 

 m, m, muscles ; cc, cceliac canal ; gr, tubular genital rachis (the nerve of 

 Muller), lying in its genital canal ; stc, the two subtentacular canals (the 

 tentacular canals of Muller), which virtually form a single canal, the parti- 

 tion between them being cribriform, as shown in fig. 7 ; tc, the true tenta- 

 cular canal, giving off alternating lateral branches to the tentacular appa- 

 ratus and the crescentic folds, at the base of which lie the saccular (sensory ?) 

 organs ss. 



Fig. 7- Longitudinal Section of the ventral portion of the Arm : — cc, cceliac canal, 

 giving off at d d lateral branches to the pinnules ; stc, subtentacular 

 canal, divided from its fellow by cribriform partition. The section has not 

 laid open the true tentacular canal ; but the orifices by which it communi- 

 cates with the tentacular system of the near side are seen at t t, and those 

 leading into the bases of the groups of tentacles of the off side are seen 

 at f f. 



Fig. 8. Transverse Section of decalcified Spermatigerous Pinnule : — a, organic basis of 

 calcareous segment ; b, axial cord ; cc, cceliac canal ; t, testis, lying within 

 a dilatation of the genital canal gc, and developed (like the ovary shown in 

 fig. 9) from a peduncle given off from the genital rachis ; stc, single subten- 

 tacular canal ; tc, true tentacular canal ; s s, saccular (sensory ?) organs. 



Fig. 9. Longitudinal Section of decalcified Ovigerous Pinnule :—a a, organic basis of 



