REPORT ON THE SIPHONOPHOR^E. 259 



face of tbe spirally coiled up trunk. When we regard the latter from below, after the 

 detachment of the siphons, the remaining pedicles of these form an innermost spiral line 

 (fig. 12, sjj) inside the spiral corona of gonodendra. In Stcphanospira these pedicles 

 were regarded by Gegenbaur as the siphons themselves (10, Taf. xxxii. fig. 53, e). In 

 spirit specimens of Discolabidee the siphons are usually all detached from £heir pedicles, 

 which remain as short conical prominences connected with the trunk (compare 6, pi. iv. 

 fig. 5). The body proper of the siphon consists of the usual three segments. The 

 proximal basigaster is very large and occupies in the contracted siphon about its basal 

 half; its thickened wall is full of small cnidocysts and surrounds a narrow cylindrical 

 cavity (6, pi. iv. fig. 5). The stomach proper is very dilatable, usually ovate or spindle- 

 shaped, and exhibits either hepatic ridges, or instead of these numerous glandular villi 

 developed from its thickened entoderm. The distal proboscis is cylindrical, very con- 

 tractile, and exhibits usually eight, twelve, or sixteen parallel longitudinal muscle-bands ; 

 it opens distally by a mouth which is very dilatable and may be expanded in the form of 

 a circular or slightly lobate suctorial disc. Often this distal part is turned over like the 

 inverted finger of a glove (6, pi. iv. figs. 4-6). 



Tentacles (PL XIX. fig. 1 ; PL XX. figs. 13, 16, t, 14).— The single tentacle, which 

 is attached to the pedicle of each siphon, near to the insertion of the basigaster, is in all 

 Discolabida? very long and beset with a series of very numerous and large tentilla. The 

 cnidosac of the latter has a peculiar structure, differing from that of all other Siphono- 

 phorss. The fully-developed tentillum is composed of two segments only, a very large 

 pedicle and a large involucrate cnidosac ; the third and distal segment, the terminal 

 filament, has disappeared. The pedicle again is often divided into two portions, a thin 

 cylindrical proximal tube, and an inflated vesicular distal sac, usually club-shaped or 

 pyriform. The cnidosac (sacculus or urticating knob) is ovate, spindle-shaped, or 

 pyriform, bilaterally ysmmetrical, with a more convex dorsal and a less convex or even 

 concave ventral side ; it contains, included in a double involucre, a very long cnido- 

 band or urticating chord, coiled up in several spirals. The latter is composed of 

 innumerable small, paliform cnidocysts, and of two lateral series of large ensiform or 

 spindle-shaped cnidocysts. These latter are placed at the distal end of the vesicular 

 cnidosac, whilst they are situated in the other Siphonanthse usually at its proximal end. 



This apparent anomaly, and the divergence in structure from the normal form, is fully 

 explained by the development of the cnidosac ; it passes during its ontogeny through 

 different stages, which are represented by the permanent cnidosacs of the genera Circalia, 

 Stephanomia, Halistemma, and Agalmopsis. The simple cylindrical tubule of the 

 youngest tentillum becomes divided into the three usual portions, the pedicle, the 

 cnidoband, and the terminal filament. The middle one of these is spirally coiled up as a 

 simple and naked spiral cnidoband. The distal portion of the pedicle becomes inflated, 

 forms a campanulate fold around the top of this band, and grows around it entirely, 



