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



attached to the distal end of pedicles of about the same length. These pedicles (fig. 7, sp) 

 are slender cylindrical tubes, very contractile, arid covered with a series of small bracts. 

 (The insertions of the detached bracts are visible in fig. 6, sp.) Usually four larger 

 bracts (comparable to a quadripartite umbrella) arise from the base of the pedicle' 

 and cover its whole length (fig. 7, b). The siphon itself has a subspherical thick- 

 walled basigaster, the cnidocysts of which are sometimes arranged on four square radial 

 plates (figs. 7, 8, sb). The ovate stomach (sm) possesses sixteen red longitudinal liver- 

 ridges, which are disposed regularly in a very remarkable manner (fig. 7, sh). Four 

 larger perradial ridges extend throughout the whole length of the stomach, while four 

 interradial, alternating with them, are shorter ; and between the former and the latter 

 are interpolated in the basal part of the stomach eight smaller adradial ridges. The 

 contractile proboscis (sr) has four stronger longitudinal muscular bands. Its distal 

 mouth exhibits sometimes eight, at other times sixteen, distinct lobes (fig. 8, so), which 

 are separated in pairs by constrictions and armed with cnidocysts (fig. 9). 



Tentacles (figs. 1, 7, t, 8, t, 23). — The single tentacle, which arises from the basigaster 

 of each siphon (at the distal end of the long pedicle, fig. 8, sp), is very long and strong, 

 distinctly articulate, and beset with a series of very numerous tentilla which arise from 

 the equidistant nodes (fig. 7, t). Each tentillum (fig. 23) is composed of three parts, a 

 thin pedicle (ts), a large spiral cnidoband (tie), and a long slender terminal filament (tf). 

 The spiral cnidoband (or " cnidobattery ") is naked, without involucre, has usually four 

 open spiral turnings (like a corkscrew), and is composed of innumerable small paliform 

 cnidocysts, with a lateral series of larger ensiform cnidocysts on each side. The peculiar 

 arrangement, exhibited by the small fusiform cnidocysts in the terminal filament, is 

 represented in fig. 23a from its proximal part, figs 23b and 23c from the middle parts, 

 and fig. 23d from the distal part. 



Cystous (PI. X. fig. 19). — The cystous or anal vesicles, one of which arises from the 

 trunk of the siphosome between every two siphons, are smaller than the latter, but larger 

 than the neighbouring palpons. Each cyston is composed of four segments, which are 

 comparable to those of the simdar siphon. The first segment is a slender and thin 

 pedicle (qp), not covered with bracts, and annulate towards the club-shaped distal end. 

 The second segment is a thick-walled hemispherical basigaster, with thickened exoderm, 

 full of cnidocysts ; it bears the long palpacle (r). The third segment (fig. 19, q) is a long 

 thin-walled cylindrical tube, comparable to the stomach of the siphon, but without the 

 characteristic liver-ridges of the latter ; it is separated by an annular constriction from 

 the basigaster at the proximal, and from the colour-gland at the distal end. The fourth 

 and last segment of the cyston is the colour-gland (chromadenia), a pyriform or conical 

 vesicle of a dark red colour, with a terminal mouth-opening, or rather an anus. Its 

 thick glandular entoderm secretes a mass of red pigment-granules, which often fill up and 

 expand the terminal vesicle. When the animal is attacked or irritated, it opens the anus 



