EEPORT ON THE DEEP-SEA MEDUSAE. CV 



that it is only its axial or proximal part which really deserves this name, whilst its 

 abaxial or distal part rather corresponds originally to the subumbral wall of the coronal 

 sinus and the four perradial pouches at its proximal margin, which have become merged 

 in the central stomach in consequence of the dissolution and resorption of the four 

 interradial cathamma. The delicate gastrogenital membrane is frequently (namely, in 

 the Pelagidse and Cyaneidaa) evaginated downwards out of the gastral cavity (Hke a 

 hernia), and forms four pendent gastrogenital pouches, in the bottom of which the four 

 frill-shaped genital bands lie (" extra versio gonadum," Pis. XXX., XXXI. ; System, p. 

 470, taf. xxx.). In most Rhizostomaa, on the contrary (and also in the Aurelida?), the 

 thin gastrovascular membrane invaginates inwards into the gastral cavity (like a replaced 

 hernia "intraversio gonadum," System, p. 470, taf. xxxiv.-xl.). If the four invaginated 

 inner gastrogenital pouches approach each other in the centre so that they touch, they 

 may become fused together and enter into communication by breach of the fused walls. 

 In this way there arises the remarkable formation, which has been already described, of 

 the " subgenital vestibule," of which the roof is formed by the cruciate gastrogenital 

 membrane, the floor by the brachial disk (comp. above § 96, p. lxxvii., woodcut, figs. 

 G and H, and PI. XXXII. ; also in the System, pp. 471-473, taf. xxxviii.-xl.). These and 

 other modifications of the gastrogenital formation of the Ephyronise have already been 

 described comparatively in the System der Medusen (1879, pp. 467-473). They are all 

 derivable from the four simple horseshoe-shaped genitalia, which we find in the subumbral 

 wall of the periphery of the stomach (or of the coronal sinus) in Ephyra, the oldest and 

 simplest form of the Discomedusae (fig. Q). In this and other morphological respects, 

 Ephyra remains one of the most important types among all Medusae. 



(ZOOL. CHALL. EXP. — PART XII. — 1881.) M 



