292 THE VOYAGE OF II.M.S. CHALLENGER. 



a length of 1 metre or more. It is annulated in the same manner as the simple 

 tentacle of the Stephalidse ; but from the interval between each two annnli arises a 

 tentillum or accessory filament (PI. IV. figs. 20-22). The line in which these numerous 

 tentilla are inserted is the dorsal median line of the cylindrical tentacle. From the 

 opposite ventral median line arises a very thin and broad ligament, the suspensorium ten- 

 taculi (PL VII. fig. 42, tg); it is similar to the well-known suspensorium or tentacle-band 

 of the Physalidse; and as in these latter, the tentacle when contracted is coiled up spirally 

 around this axial ligament. The transverse section of the tentacle, when magnified, shows 

 us that the elastic ligament is composed of a solid lamellar apophysis of the cartilaginous 

 fulcrum (PI. IV. fig. 21, tl), and is covered by a single layer of exoderm-cells (e). 



The structure of the tentacle visible in the transverse section (PI. IV. fig. 21) is 

 similar to that of other Siphonanthae. The cylindrical central canal (c) is lined by a 

 simple layer of large entoderm-cells (d), and this is surrounded by a thin muscular tube 

 composed of circular fibres (mc). This entodermal plate is separated from the thicker 

 exodermal wall by a strong gelatinous fulcrum of nearly cartilaginous consistence 

 (2). The structureless fulcrum or supporting plate is surrounded in the transverse 

 section by a corona of numerous (seventy to ninety) radii ; they are the transverse 

 sections of large longitudinal radial jelly-lamella? which support the strong longitudinal 

 muscle-fibres (ml). The latter appear in the transverse section regularly arranged on 

 both sides of the lamella?, like a pinnate leaf. The outer envelope of the exoderm (e) 

 is very thick and composed of a stratified epithelium including may thread-cells. The 

 circular annuli of the exoderm, composed of the radial supporting lamella? and the parallel 

 bundles of longitudinal muscles, are not quite complete, but interrupted on the ventral 

 side by the broad elastic ligament of the tentacle or the suspensorium (tl). 



Tentilla (PI. IV. fig. 23). — The accessory filaments or tentilla of the Rhodalidae are 

 simple lateral branches of the main tentacle, arranged in a single series in its dorsal 

 median line. This series is opposed to the large, mesentery-like elastic ligament. 

 The length of the lateral branches, which commence as very small bud-like elevations in 

 the proximal part of the tentacle, increases gradually towards its distal end ; the longest 

 tentilla have a length of 5 to 10 mm. or more. The fully developed tentillum (PI. 

 IV. fig. 23) is very similar to that of Forskalia (PI. X. fig. 23). It consists of three 

 cylindrical parts, viz., a short pedicle (tb), a spiral cnidoband (tk), and a slender terminal 

 filament (tf). The short pedicle (tb) is inserted with narrow base in the interval 

 between two thickened annuli of the main tentacle (fig. 22) ; its epithelium bears only 

 very small cnidocysts. The cnidoband (tk) is armed with a strong cnidobattery, and is 

 a thick-walled cylindrical tube coiled up in several lseotropic spirals. On its ventral 

 or axial side are attached two strong parallel elastic ligaments (the so-called " angle- 

 bands," fig. 23, tl), and on both edges of these a series of very large bean-shaped or 

 ensiform lateral cnidocysts (tki), whilst the convex dorsal side of the cnidobattery bears 



