REPORT ON THE DEEP-SEA MEDUSAE. lxxvii 



extended into large evaginations, which project centifrugally to the outside (into the 

 umbrella cavity), and may be compared from their form and function to the buccal pouches 

 of many mammalia (bb). We term the thicker parts of the oral wall, which project 

 inwardly centripetally between them, the oral columns {etc). The buccal pouches are 

 most strongly developed among the Acraspedae in the Peromedusae, where they form four 

 powerful perradial archings outward of the large buccal stomach and appear inflated 

 hemispheroidally or even spheroidally (as in Periphylla, Pis. XVIII.-XXV., bb). Each 

 single inflated buccal pouch is sometimes more voluminous here than the whole central 

 stomach. The four thick intermediate, interradial oral columns (ac) project internally 

 with their axial surfaces extended like wings, in such a way, that the adradial side 

 spaces of the four buccal pouches form special niches or wing pouches behind these oral 

 wings (ad, comp. also System, p. 405, taf. xxiv. fig. 14). Among the Craspedotse the 

 buccal pouches are most strongly developed in the Trachomedusse, whose oesophagus is 

 often highly extensible. Pedis (PI. V. figs. 2-5 ; PL VI. fig. 11) has sixteen subradial 

 buccal pouches, which are developed in pairs from four perradial and four interradial 

 evaginations of the oesophagus, and are separated by eight adradial subumbral oral funnels 

 (PL V. fig. 5, id). Other Trachomedusse have eight adradial buccal pouches (formed by 

 the division of four perradial). 



§ 113. Oral lobes and oral arms (" lobi orales," al; "brachia oralia," ab). In the 

 majority of Medusae the oral margin is not simple, but its four perradial corners are 

 prolonged into four leaf-shaped oral lobes or oral arms, between which four interradial 

 oral sinus or oral incisions (" sinus orales ") project internally. The four oral lobes 

 have usually the shape of a thin oral leaf, whose delicate margins are folded more or less, 

 often very daintily, whilst a strong midrib projects in the middle (as distal end of the 

 perradial oral corner). The supporting plate of this midrib is often thickened gelatinously, 

 shaped like a groove, concave outside and convex inside. The axial inner side of the oral 

 lobes is always covered by endoderm, its abaxial outer side by ectoderm (comp. in the 

 System, 1879, the oral lobes of the Anthomedusse, taf. iii., iv. ; of the Leptoniedusas, 

 taf. viii., x., xi., xiii. ; of the Trachomedusse, taf. xvi., xviii. ; of the Narcomedusse, taf. 

 xix., xx. ; of the Stauromedusaa, taf. xxi., xxii. ; of the Peromedusae, taf. xxiii., xxiv. ; 

 of the Cubomedusse, taf. xix., xx. ; of the Discomedusse, taf. xxvii., xxx., xxxii., xxxiii.). 

 The oral lobes are termed " oral arms," if the four perradial oral lobes are very large, and 

 the intermediate oral sinus so deep that they divide the oesophagus almost, or completely 

 into four parts. These oral arms attain an extraordinary development in the order of the 

 Discomedusse, in the sub-order of the Semostomse, namely, in the " pennon-mouthed " 

 Pelagidse (System, taf. xxxi.), and Cyaneidse (System, taf. xxx.). In most Cyaneidae 

 they resemble delicate curtains with numerous folds, which are frequently larger than the 

 whole umbrella, and are therefore termed " oral curtains" (Pis. XXX., XXXL). 



§ 114. Quadripartite mouth of the Rhizostomse. The third and last sub-order of the 



