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



forming a complete external involucre. The canal of the pedicle runs along the 

 extended and convex dorsal side of the involucre, which overgrows the ventral side. 

 The axis of the spiral cnidoband, originally vertical, becomes more and more inclined, 

 is afterwards horizontal and perpendicular to the axis of the pedicle, and finally inverted 

 completely, so that the original distal end of the cnidoband is situated at the proximal 

 base of the cnidosac, on its ventral side. The terminal filament, originally the simple 

 prolongation of that distal end, is early divided into three apophyses, an odd median (the 

 terminal ampulla) and two paired lateral horns (as in Agalma, &c). But these are not 

 fully developed (being rudimentary organs) and disappear finally. Tbe basal point of their 

 original insertion remains visible at the distal end of the reflected cnidoband, near the 

 proximal base of the cnidosac, in its ventral median line. Compare the full description of 

 this interesting metamorphosis by Gegenbaur (10, p. 63, Taf. xxx.), Claus (34, pp. 295 et seq., 

 Taf. xxvi.), Keferstein and Ehlers (33, p. 10, Taf. iv.), Sars (27, Heft, iii. Taf. v.), &c. 



Pa/pons (PI. XIX. fig. 1, q; PI. XX. fig. 16, q). — The large corona of palpons, 

 which expands at the base of the nectosome and covers the entire siphosome as a 

 protective roof, is very characteristic of the Discolabidse. The tasters or palpons are in 

 this family far larger and relatively far more developed than in all the other Siphono- 

 phorse. They are not only organs of feeling and tasting, but also of capturing and 

 protecting; they were, therefore, formerly confounded with other organs; Vogt described 

 them erroneously as bracts (6), and Claus as tentacles (34). Each cormidium possesses 

 either a single or two palpons, a larger proximal and a smaller distal; and the corona, 

 therefore, is either simple or double. This difference may perhaps serve also for the 

 definition of genera, as I have employed it in my System (95, p. 41). Discolabe and 

 Stephanospira possess a simple corona of tasters, while it is double in Physophora. 

 But in this latter also usually one corona only (the upper and larger) is fully developed, 

 and the accessory (lower and smaller) corona is incomplete or rudimentar}*. The 

 development of the latter is variable in one and the same species (74, p. 15). Each 

 palpon is a spindle-shaped, cylindrical, or slenderly pyriform tube, with a simple wide 

 cavity and a very thick muscular wall; the structure of the wall is similar to that of the 

 trunk ; both the entoderm and exoderm are glandular ; the fulcrum bears inside a plate 

 of ring-muscles, outside numerous high radial folds which are covered with longitudinal 

 muscles. The consistence of the fulcral plate is nearly cartilaginous (compare 74, p. 43. 

 Taf. v. fig. 7). The pointed and closed distal end of the palpon is provided with a 

 corona of large cnidocysts and tasting cells. The dilated and obliquely truncated 

 proximal end is apposed by a broad elliptical articular face to the facette of the 

 siphosome described above, but connected with the latter by a very small pedicle only. 

 The palpons, therefore, are very easily detached from the siphosome, and a small pore 

 only in the middle of each articular facette indicates the place of the narrow canal which 

 connected the wide cavities of the trunk and of the palpon (PL XX. figs. 9-13, cq). 



