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



base to the inferior part of the dorsal side of the pneumatophore and placed in the sagittal 

 plane. In Stephalia (PI. VII.) it is of the same size as a nectophore ; in Rhodalia 

 (PL III.) much smaller. The comparison of the vertical sagittal section (PI. V. 

 fig. 24 ; PL VII. fig. 40) and of the vertical frontal section (PL V. figs. 25, 26) 

 proves that the aurophore possesses a singular medusoid structure ; it is pierced by 

 a cylindrical central canal, the auroductus (la) running in a nearly horizontal direction and 

 opening inside into the cavity of the pneumatophore by the auropyle (figs. 16, 24, li), 

 outside by an external mouth, the aurostigma (figs. 15, 24, 40, lo). The auroduct or 

 central canal is lined inside by a thick-walled peculiar tube, the pistillum ; while it is 

 surrounded outside by a number of radial chambers, which are separated by septa and 

 communicate with the pericystic cavity of the pneumatosaccus. 



The remarkable structure of the single parts of the aurophore, compared with the 

 corresponding parts of the nectophores and the pneumatophore, makes it probable that 

 the aurophore is a modified nectophore, transformed into a pneumadenia ; in this case it 

 has the morphological value of a medusoid person. On the other hand, it is possible 

 that it was originally only a secondary organ of the pneumatophore, a basal apophysis of 

 the air-funnel (PL VII. fig. 50). Perhaps its outer opening corresponds to that which 

 the Discolabidae exhibit at the base of the pneumatophore. 



The transverse section of the aurophore (PL V. fig. 25, in the proximal part; fig. 26, 

 in the middle part) exhibits in its outer wall from outside to inside the following five 

 strata: — (l) A simple exodermal epithelium (e) composed of rather flat small cells; 

 (2) a muscular plate composed of longitudinal niuscle-fibrillse, which are probably direct 

 prolongations of the epithelial cells ; (3) a thin cartilaginous fulcra! plate (z), much 

 thinner than the same fulcrum of the pneumatophore, but very firm and elastic, consisting 

 of structureless jelly, strongly stained by carmine ; (4) a thin layer of ring-muscles ; 

 (5) a thick entodermal epithelium, composed of very large cylindrical cells. 



The same five strata recur also in the inner wall of the aurophore, following, 

 however, in the inverse order ; the entoderm lying outside, the exoderm inside. The 

 latter surrounds the central cavity of the aurophore, which is filled by the pistillum; 

 between them is visible the vagina pistilli, a structureless tube (If) intensely stained by 

 carmine; it seems to be a chitinous cuticular membrane, formed by a direct prolongation 

 of the pneumatocyst (pf)- 



The outer wall of the aurophore (exumbrella) and the inner wall (subumbrella) are 

 connected by a variable number of radial septa ; and by these are separated wide radial 

 chambers (figs. 24—26, Ir). These correspond probably to the radial pouches of the 

 pneumatophore in the Physonectse, and to the radial canals of the medusoid nectophores ; 

 they are, however, much wider than the latter. Their number is variable ; usually 

 between eight and twelve. In the middle part of the aurophore (in transverse sections 

 which cut the pistillum at right angles in its middle part) eight to twelve radial 



