lxvi 



THE VOYAGE OF H.M.S. CHALLENGER. 



sometimes eight adradial) reproductive bands are developed. The gelatinous support- 

 ing plate of the subumbrella is often thickened round these genitalia in the form of a 

 firm, cartilage-like subgenital ring (" annulus subgenrfcalis "). If the genital band 

 increases considerably and the delicate gastrogenital membrane round it becomes folded 

 repeatedly, the latter may undergo a double change of position. It either passes below- 

 through the firm subgenital ring, which does not extend in an equal degree, into the 

 umbrella cavity, thrusts itself out like a projecting hernia and so forms four pendant ex- 

 ternal gastrogenital pouches whose cavities are lined by endoderm (" extraversio gonadum," 



Fig. G. Cannorlriza connexa (Discomedusje, Versuridie). 



Adradial section, (ug) Gelatinous umbrella, (gc) Central stomach, (gg) Bottom of the central stomach 

 (gastrogenital membrane with the genitalia, s). (ir) Subgenital porticus. (ah) Braehiferous plate. 

 (ap) Arm pillars, (cd) Pillar canals, (ga) Buccal stomach, (ab) Oral arms (adradial). (cb) 

 Brachial canals, (an) Funnel frills (sucking mouths). 



System, p. 470), as, for example, in the Cyaneidse (Pis. XXX. XXXL, gg) or, reversed, 

 the increasing folded gastrogenital membrane, along with the genitalia attached to it, 

 does not pass through the subgenital ring, but invaginates into the central gastral cavity, 

 like a replaced hernia (as, for example, in the Aurelidse, System, taf. xxxiii. fig. 7). It 

 then forms four " inner subgenital cavities," lined with the ectoderm of the subumbrella 

 (" introversio gonadum," System, p. 470). These are, however, merely flattened funnel 

 cavities ; the " ostium subgenitale," which may be compared to the " hernial opening " 

 ("porta hernise subgenitalis"), is the narrow opening of the subgenital ring, which leads 



