784 THE ANIMAL KINGDOM. 



sense-bodies, tentaculocysts or rhopalia, are cylindrical, straight or curved 

 organs, with the following structure. The endoderm at their apex forms a 

 mass of nucleated cells or protoplasm, imbedding a variable number of 

 calcareous otoliths, which do not however contain Lime Carbonate. The 

 ectoderm cells of the apex are flattened (? ciliated), those of the sides are 

 more or less columnar (i) supporting cells, (2) sense-cells, furnished with 

 sense-hairs, and prolonged basally into filaments in connection with gan- 

 glion cells which lie among the sub-epithelial nerve-fibres (Claus, von 

 Lendenfeld). A patch of visual pigment is commonly present on the 

 dorsal aspect of the organ near its base, but in Nausithoe and its congeners 

 there is a ventral eye provided with a lens, with sense-cells, pigmented 

 supporting cells and ganglion cells (?). The sense-bodies are usually pro- 

 tected by a dorsal, i. e. exumbrellar covering-piece or hood, sometimes of 

 large size, and by two lobes which curve round it below, and are developed 

 from the inner edges of the bifid Ephyra lobes. There is often a depres- 

 sion in the exumbrella above the base of each sense-body. It is lined by 

 ciliated cells, and is supposed to test the character of the sea-water, i. e. to 

 exercise a gustatory or olfactory function l . The sense-bodies appear to be 

 so many nerve-centres, and they are connected to a sub-ectodermic plexus 

 of ganglion cells in the subumbrella, and control the movements of the 

 animal. 



The exumbrellar and subumbrellar walls of the peripheral part of the 

 gastric cavity fuse from place to place with the formation of a gastral 

 lamella, leaving pouches, simple or branched vessels, or retia, and there is 

 very generally a circumferential canal 2 . The gastric filaments are motile 

 cylindrical processes disposed in groups (phacelli) on the subumbrellar 



1 In Aurelia and Cyanea Annaskala the base of the marginal bodies is surrounded by sensory 

 epithelium, nerve- fibrils and ganglion cells. There is also a similarly constituted elongated patch 

 extending centripetally from near the base of the marginal body on the surface of the subumbrella. 

 C. Annaskala and C. capillata possess sensory patches also upon the inner and outer faces of the two 

 lateral protective lobes of the rhopalia. A layer of nerve-fibrils underlies the olfactory epithelium 

 which in C. Annaskala at least is scarcely distinguishable from that of the sensory bodies them- 

 selves. 



The number of rhopalia is more than 8 in a few instances ; 19-22 occur in Atolla ; ^I'vaCollaspis 

 (Cannostomae) ; 12 are found in the Semostome genera Phacellophora, Patera and Medusina, and 

 the Rhizostome genus Polyclonia; 16 in the Rhizostome Cassiopeia. Von Lendenfeld has observed 

 that the young Ephyra of the Rhizostome Stylorhiza punctata has 24 ; reduced in an older Ephyra 

 to 16, and finally to 8 ; see Z. A. vii. pp. 430-31. He does not mention that its Scyphostoma 

 shows any peculiarity : cf. Proc. Lin. Soc. N. S. Wales, ix. p. 297, under Phyllorhiza p^mctata ; and 

 for figures of the bell-margin of the Ephyra, ibid. PI. V. 



* The gastral lamella formed by the cohesion of the exumbrellar and subumbrellar walls of the 

 gastric cavity consists of a single layer of cells in the fully formed central region of the bell, and 

 sometimes, if not always, of a double in the peripheral growing parts. It appears to extend at its 

 edges as the bell grows in size, and vessels are excavated between its two layers. See von Lenden- 

 feld, Z. W. Z. xxxvii. p. 490, and Haeckel, ' Deep-sea Medusae,' Challenger Reports, iv. PI. XXV. 

 Figs. 8 and 10. Indications of its double nature are always to be discerned in the Cubomedusan 

 Charybdaea, according to Claus. 



