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



number only amounts to from 120-160. The filaments are otherwise strong, full of 

 glands, and often tongue-shaped or swollen like a club at their free end, 2-3 mm. 

 long, 10-14 mm. thick. 



The gastral openings (figs. 3, 6, go) are four horizontal transverse fissures, 4 mm. in 

 breadth, which lie at the distal end of the four cross limbs of the bottom of the stomach 

 and lead from it into the coronal sinus (cs). The upper lip, or the upper (umbral) 

 margin ofthe transverse fissure, is somewhat concave and formed by a slightly projecting 

 ridge of the endodermal wall of the gelatinous umbrella. The lower lip, or the lower 

 (subumbral) margin of the gastral opening, on the other hand, is slightly convex, and 

 formed by a thickened crescentic ridge of the - subumbrella (at the proximal margin of 

 the coronal sinus (figs. 3, 6, go). This lower lip can fab! like a valve over the other and 

 so shut off the coronal sinus from the oesophagus ; it corresponds to the perradial 

 pouch lobes of the Cubomedusse. The two lateral oral angles of the gastral openings 

 are bounded by the darkly-pigmented ridges of insertion or roots of the genital fulcra 

 (" sterigmata," st, fig. 3). 



The peripheric coronal intestine of Atolla, which only communicates with the central 

 principal intestine by the four narrow perradial gastral openings, resembles that of 

 Nausithoe and Nav/phanta on the one hand, and that of Periphylla and Periphema on 

 the other. It is divided into two sections, the proximal coronal sinus and the distal corona 

 of pouches, by a subumbral circular furrow, corresponding exactly to the exumbral coronal 

 furrow (ec), and is only separated from it by the thinnest part of the gelatinous umbrella 

 (ec). The large coronal sinus (" sinus coronaris," fig. 3, ec) corresponds to the narrower 

 sinus of Nauphanta (PI. XXVIII. fig. 14, cs) and the broader sinus of Periphylla (Pis. 

 XX. -XXII., cs). Whilst, however, in both these species it stands vertically (with an 

 upper and lower margin and an inner and outer surface), in Atolla it has assumed a 

 horizontal position (with an inner and outer margin and an upper and lower surface), 

 corresponding to the strong depression of the discoid umbrella. It forms here a circular 

 hollow space, 6-7 mm. broad and 1-2 mm. high. The upper or umbral wall of the 

 coronal sinus forms the flat endodermal surface of the corona of teeth of the central 

 gelatinous disk ; it also shows externally a fine coronal furrow, from which nnmerous 

 fine radial indentations project centripetally inwards (fig. 3, zw). The lower or 

 subumbral wall forms the genital zone of the subumbrella, which is composed of the 

 eight broad adradial genitalia and the eight narrow deltoid muscles alternating with 

 them, four smaller perradial (rnd') and four broader interradial (md"). The inner or 

 axial margin of the coronal sinus is formed by the four perradial gastral openings 

 (through which it communicates with the central stomach) and by the four abaxial base- 

 lines of four interradial septal plates (kt) alternating with these. The external or 

 abaxial margin is composed of the tangential transverse fissures by which the pouches of 

 the corona of pouches open into the coronal sinus. 



