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



colourless bracts is usually more or less cartilaginous, sometimes soft ; it is thickened 

 in the middle part and often towards the distal edge. The proximal base tapers 

 towards the small movable pedicle, which attaches the bract to the trunk. 



Siphons.^— Each cormidium of the Agalmidae possesses a single siphon only, and 

 this is placed originally always (and in the ordinate cormidia permanently) at its distal 

 or lower end. The four segments of the siphon exhibit a varying degree of develop- 

 ment. The pedicle (sp) is usually short, but sometimes prolonged (e.g., in Lychnagalma). 

 The basigaster (sb) is usually small, sometimes rudimentary. The stomach (sm) in most 

 Agalmidae is large and provided with longitudinal equidistant liver-ridges, usually of 

 a red or brown colour. Their number in most Agalmidae is eight, sometimes four 

 (Anthemodes, PL XV. fig. 7), twelve (Cuneolaria), or sixteen (Halistemma, 6, pi. viii. 

 fig. 1). Usually the hepatic ridges are continuous glandular bands, but sometimes 

 composed of single villi arranged in longitudinal series. The proboscis (sr) is always 

 a very muscular cylindrical tube, highly expansible. Its distal mouth is extremely 

 variable in form and size; it may be expanded in the form of a very large and thin- 

 walled suctorial disc, sometimes circular, at other times polygonal (often octagonal). 

 Its edge is usually armed with cnidocysts. 



Tentacles. — The single long tentacle, which is attached to the base of each siphon, 

 exhibits the same essential structure in all Agalmidae, but shows great variety in the 

 form of its equidistant lateral branches. The various forms of these tentilla have been 

 already employed by Eschscholtz (1829) and afterwards by Huxley (1859) for the 

 distinction of genera. The simplest and most primitive form is found in Halistemma ; 

 the cnidoband is a simple, thickened, spirally convoluted dilatation of the middle 

 part of the tentillum, with a double elastic band (or angle-band) on its ventral side, and 

 a strong cnidobattery on the dorsal side ; the terminal filament is a simple thin tubule, 

 similar to the pedicle. Four other genera (Stephanomia, Phyllophysa, Anthemodes, 

 and Cupidita) have the same form of the tentillum, but with this difference, that a 

 campanulate involucrum arises from the distal end of the pedicle and encloses the 

 proximal part of the cnidoband (PL XV. fig. 11). This involucrum is complete in four 

 other genera (Crystallodes, Agalma, Cuneolaria, and Agalmo-psis) ; the simple terminal 

 filament in these is replaced by a tricornuate appendage, an odd median terminal 

 ampulla, and two paired, often spirally coiled lateral horns (PL XVII.). The highest 

 degree of development, finally, is attained by Lychnagalma; the long cnidoband, enclosed 

 in a complete involucrum (or cnidosac), bears at its distal end a very large, hydrostatic, 

 terminal ampulla surrounded by a corona of eight radial horns (PL XVI.). 



Paljwns. — All the Agalnridae possess a number of hydrocysts on the siphosome, either 

 true (mouthless) palpons, or excreting cystons (with a mouth). The distinction between 

 them is often difficult and requires further accurate observations. Usually each cormidium 

 (with a single siphon) possesses several (four to six or more) palpons ; but sometimes 



