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



equidistant radial muscles run divergently from the apical centre to the basal periphery, 

 and these are crossed by about a dozen strong circular muscle-rings of equal breadth. 

 The subspherical aurophore (I) is about the same size as a nectophore. The number of 

 neetophores in this species, judging from the insertions of their pedicles, may be twenty 

 or thirty, and they seem to be arranged in a double corona, a superior and an inferior. 

 But the majority of the neetophores were detached in the two specimens examined, 

 and a more accurate examination of their arrangement is required. 



Siphosome. — The complete siphosome, including the retracted appendages, is nearly 

 spherical, and may be about the same size as the nectosome. The sagittal section is 

 very similar to that of Stephalia (PI. VII. fig. 40) ; but the central axial canal (ac) is 

 wider, and the terminal protosiphon larger (figs. 32, 33, a/p). The number of cormidia 

 may be sixty to eighty, and they seem to be arranged in a condensed low spiral. The 

 apical part of the trunk is surrounded by a corona of eight larger cormidia, distinguished 

 by very large annulated tentacles, with a slender terminal filament (figs. 34-38). The 

 other cormidia have slender simple tentacles, similar to those of Stephalia. Each 

 gonodendron (g) bears a large palpon (q). 



Family XIX. Ehodalidj;, Haeckel, 1 i 



Rhodalidx, HkL, System der Siphonophoren, p. 43. 



Definition. — Auronectse without a permanent central canal in the axis of the bulbous 

 trunk, and without a permanent primary mouth at its basal pole. Tentacles with a series 

 of tentilla or lateral branches. 



The family Rhodalidse comprises the larger and superior forms of Auronectse, with 

 branched tentacles, without permanent protosiphon and primary mouth. I was able to 

 examine accurately only a single genus and species of this interesting family, Rhodalia 

 miranda (Pis. I.-V.). A second closely allied genus seems to be Auralia, differing from 

 Rhodalia in the simple corona of neetophores, and in the possession of a large central 

 cavity in the centre of the subglobular trunk of the siphosome. The general composition 

 of the corm, the structure of the nectosome and of the -siphosome, and the form of 

 the single organs composing them, have been described above (p. 281). It need 

 only be added here, that the Rhodalidaa, regarded from a phylogenetic point of 

 view, represent the younger and more highly developed forms of Auronectse. The size 

 of the whole corm, as well as of all its single parts, is far larger, and the number of the 

 cormidia and their component persons and organs far more considerable, than in their 

 ancestral forms, the preceding Stephalidse. The central axial canal of the latter, 

 and its terminal mouth, have either disappeared, or they cannot be distinguished 

 from the other siphonal cavities and mouth-openings. The tentacles produce a series 



