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



gonodendra arise besides the siphon (fig. 2) ; more rarely three or even four gonodendra 

 arise separately from one cormidium. The long tubular gonopalpon (PI. I. fig. 2, r; 

 PL IV. fig. 15, r, fig. 18, q), as the distal prolongation of the original stem of the 

 gonostyle, seems to be always single in each cormidium. 



All the corms examined had lost the nectophores, the siphons, the tentacles, and the 

 gonopalpons, with a few exceptions. All these detached parts were found beside the 

 corms in the bottle. But fortunately in some specimens one or two of these organs 

 had remained in their natural attachment, so that it was possible to determine their 

 probable natural position ; so, e.g., a single n«ctophore (n) in PI. IV. fig. 16, and a single 

 gonopalpon in figs. 2 and 18. All the tentacles were attached to the basigaster of the 

 siphons, which were separated by self-amputation from their pedicles remaining on the 

 trunk (compare above, p. 290). On the structure of all separate parts compare the 

 general description of Auronectse (pp. 281-296). 



Additional Note on the Deep-Sea Life of the Auronectse. 



The new and most interesting group of Auronectse, which is one of the most splendid 

 discoveries of the Challenger, and described in the preceding pages (pp. 281-304, Pis. 

 I. -VII.), represents a new order which is adapted in a most remarkable manner to deep-sea 

 life. The Auronectse differ from all other Siphonophorse in the peculiar structure of the 

 bulbous cartilaginous trunk traversed by a peculiar network of canals, in the singular 

 shortening of the vertical main-axis, and prolongation of the horizontal transverse axis. 

 Upon this vertical depression of the trunk depends the peculiar development of the 

 densely crowded cormidia. But the most striking peculiarity is the extraordinary 

 development of the swimming apparatus, the voluminous pneumatophore, the powerful 

 horizontal corona of radially expanded nectophores, and particularly the singular 

 aurophore, wanting in all other Siphonophorge, and acting probably as an important 

 gas-secreting gland or a pneumadenia. All these striking characters together make it 

 very probable that the Auronectse are permanent deep-sea Siphonophorse, which may 

 move up and down within certain limits of depth, but never come to the surface. 



