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



3-6, to), where each tentacle does not arise from the base of a siphon (as is usually the 

 case in the Siphonanthse) but from the base of a large palpon, which is connected by 

 a common pedicle only with the base of the siphon. Huxley, therefore, calls these 

 palpons not hydrocysts, but basal sacs of the tentacles (similar to the ampullae of 

 the ambulacral feet in Echinoderms). It may be that these basal ampullae are only 

 secondary diverticula of the base of the tentacle, and have the morphological value of a 

 subordinate organ. On the other hand, it is possible that each cormidium of the 

 Physalidse originally bore two polypites each with a tentacle ; one of these (the siphon) 

 has preserved the mouth and the hepatic villi, but lost the tentacle ; the other, conversely, 

 has lost the former organs and preserved the latter (the palpon). 



Tentacles. — The capturing filaments are arranged in the majority of Cystonectse in 

 the same manner as in all other Siphonanthse, a single tentacle arising from the basal 

 pedicle of each siphon. A single exception is formed by the Physalidse, in which the 

 tentacles arise from the base of peculiar palpons, as has just been mentioned (PL XXVI. 

 figs. 2-6). The tentacles are generally long and vigorous, very muscular tubules, 

 sometimes simple, at other times branched. They are simple, not branched filaments in 

 the genera Linophysa (Rhizophysidse) and Salacia (Salacidse), and in all Physalidse. 

 In all the other genera the tentacles are branched, and bear, usually, a single series of 

 equidistant tentilla or lateral filaments. These latter are simple thin tubules, beset with 

 scattered cnidoblasts in the genera Cystalia, Epibulia (PL XXII.), Aurophysa, and 

 Nectophysa (PL XXIII. ). The distal end of the tentillum is trifid (with a terminal 

 ampulla and a pair of lateral horns) in the genera Cannophysa (PL XXIV.) and 

 Pneumophysa. The genus Rhizophysa is distinguished by the possession of two or three 

 different kinds of tentilla ; between the trifid forms being intermingled peculiar large 

 hand-shaped or palmate tentacles which bear an ocellus. 



The cnidocysts of the tentacles are spherical in most Cystalidse (PL XXI II. fig. 7), and 

 do not exhibit that variation in form seen in the Physonectse. Their arrangement is 

 variable in the various groups. Usually each tentillum bears a multiple series of cnido- 

 cysts on its dorsal side whilst the opposite ventral side is covered with palpoblasts 

 (PL XXIII. fig. 6, tw). The simple tentacles of the Physalidse (PL XXVI. fig. 6, t) and 

 of the Salacidse (PL XXV. fig. 5, t) bear a long series of large reniform cnidonodes on 

 their dorsal side (compare Huxley, 9, pi. x. figs. 11, 12, &c). Each cnidonode embraces 

 the tentacle with the concave ventral side, and bears on the convex dorsal side a cushion 

 of cnidocysts. They develop in the same manner as the tentilla of branched tentacles 

 and contain a cavity, as a diverticulum of the tentacular canal. Each kidney-shaped 

 cnidonode, therefore, may be regarded as a very short and broad tentillum. 



Gonophores. — All Cystonectse possess monoecious corms, monoclinic cormidia, and 

 monostylic gonodendra, male and female gonophores arising from the same branched 

 gqnostyle. The peculiar form and composition of the clustered gonodendra seems to be 



