REPORT ON THE DEEP-SEA MEDUSAE. lxvii 



from the coronal cavity of the umbrella into the four funnel cavities (compare the 

 detailed description in the System der Medusen, 1879, pp. 467-473). Whilst the four 

 subgenital cavities remain separate in most Discoinedusae furnished with them (Tetra- 

 demnise), in part of the Khizostomae (Monodemniae) they are fused in the centre into a 

 single common " subgenital vestibule." 



§ 96. Subgenital vestibule (" portieus subgenitalis, syndemnium," iz). The peculiar 

 and remarkable hollow space, which we have termed " portieus subgenitabs " (System, 

 1879, p. 472), is only found in the middle of the subumbrella in two families of the 

 Rhizostonue, the Versuridse (System, taf. xl.) and the Crambessidse (System, taf. 

 xxxviii., xxix.), which we have therefore united into the section of the Mono- 

 demniaB. This central subgenital vestibule has arisen from the four interradial, 

 subgenital cavities already described, growing centripetally as far as the middle of the 

 central gastral space, and entering there into immediate communication (PI. XXXII. , and 

 woodcut, fig. G). The delicate gastrogenital membranes (gz) which form the thin wall 

 of the invaginated subgenital pouches, touch in the central axis of the gastral cavity and 

 become fused together ; these points of fusion are then broken through and the four 

 subgenital cavities, which were originally separated, are consecpiently fused into one. 

 The cruciform central subgenital vestibule formed in this way (PI. XXXII, fig. 2, iz) is 

 completely lined by the ectoderm of the subumbrella, and only opens to the outside by 

 four interracbal portals, the "subgenital ostia" (figs. 1, 7,ig). Its upper wall or the 

 vestibule roof (" paries portieus gastralis ") is formed by the delicate gastro genital 

 membrane (gg) which separates it from the overlying gastral cavity (gc) and bears 

 the four genitalia (s) ; its lower wall, or the " vestibule floor," is formed by the peculiar 

 brachiferous disk (" discus brachiferus ") from which the eight adradial oral arms of the 

 Rhizostoinas depend, and in the middle of which below we find the suture of the oral 

 cross (PI. XXXIL, figs. 2, 6, 7, ah). The two walls are only connected by the four 

 perradial vestibule pillars (" pilastri," ap). These are four strong gelatinous columns, 

 placed between the four narrower or wider subgenital openings. The four simple pillar 

 canals (fig. 2, cd) which represent the only connection between the upper central 

 stomach (gc) and the lower buccal stomach (go) along with the arm canals (eb) 

 proceeding from it, run perradially upwards in these columns. 



