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



Pectyllis, but is easily distinguished by the blind centripetal canals running from the 

 circular canal, and also by the peculiar side pouches in the periphery of the mouth, and 

 the oral funnels alternating with these (PI. V. figs. 2-5; PI. VI. fig. 11). The central 

 oesophagus hangs down from the fundus of the umbrella cavity till past the middle of 

 it in the shape of a quadrangular tube beset above the oral opening with eight pairs of 

 side pouches. The eight radial canals running out from the basis of the stomach unite 

 at the umbrella margin into a circular canal, from which run numerous shoi't blind cen- 

 tripetal canals (PL VI. fig. 11). 



The quadrate oral opening (figs. 3, 4, al ; fig. 11 in the middle) is surrounded by 

 a very muscular protuberant oral margin, whose surface has strong folds of the circular 

 muscle (fig. 3, me). These folds are divided into four interradial groups by four 

 perradial longitudinal muscles, ending in the four short heart-shaped oral lobes 

 (fig. 3, al). Above this muscular oral margin (which is probably very ductile, and 

 adapted for adhesion by suction) appears a very prominent circle of sixteen side pouches 

 (" bursse buccales," figs. 2-5, bb). These form hemispherical, or, more properly, semi- 

 oval evaginations of the gastral wall, and hang together in pairs in such a way that eight 

 pairs appear as oral bifurcated terminal shoots of the eight gastral grooves (gs) ; of 

 these longitudinal grooves of internal wall of the stomach, which proceed above in the 

 fundus of the gastral cavity (figs. 3, 4, cr). Each two pairs of side pouches are divided 

 by a peg-shaped oral funnel (infundibulum orale, figs. 2, 4, 5, 10). These conical 

 adradial oral funnels are quite peculiar invaginations of the gastral wall, in a certain 

 measure " internal side pouches " unknown to me in any other Medusa. Their conical 

 cavity, which is ccecal at the point, is lined by the ectoderm, and opens into the umbrella 

 cavity, whilst these " external side pouches" (bb) are lined by the endoderm, and open 

 into the oral cavity. Such " external side pouches" are unknown to me in any other 

 Craspedota, but they occur in the Periphyllidae among the Acraspeda (compare below). 

 The ectodermal external wall of the external side pouches is coloured with violet-brown 

 pigment, and has a broad milk-white dentated longitudinal striation in the middle. 

 The endodermal covering of the oral funnels is coloured milk-white, and sharply con- 

 trasted with the dark violet periphery of the oral cavity. The upper part of the gastral 

 cavity into which the gelatinous sphere of the umbrella (fig. 2, vb> % ) projects, appears 

 eight-rayed in the transverse section (fig. 6), as eight adradial longitudinal folds running 

 from the eight oral cavities project inwardly between the eight concave gastral groups 

 into the lumen of the central cavity (g). Compare the perradial longitudinal section 

 (fig. 4). 



The eight radial canals (figs. 11, 20, cr) which run from the basis of the stomach to 

 the umbrella margin, and there open into the circular canal, as well as the circular 

 canal itself (cr), and the blind centripetal canals proceeding from it, are not cylindrical 

 tubes, but flattened band-like vessels which are sharply distinguished by then milk-white 



