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



a canal in transverse section (fig. 3). The distal (lower) half of the lower arm consists of 

 a frilled, tassel-shaped bunch of tufts, with a projecting, pointed, triangularly pyramidal 

 terminal appendage or gelatinous knob at its end. The bunch of tufts is composed of 

 three strongly frilled, many folded leaves, forming the distal process and expansion of 

 the three angles of the arm. One of these three arm frills lies axially on the inner side of 

 the arm, and appears as the distal part of the originally simple ventral frill, whose 

 proximal part is an arm of the eight-rayed tuft rosette of the oral area ; these two are 

 separated from one another by the broad interspace of the naked upper half of the arm. 

 The other two arm frills lie in pairs on the outer side of the arm, and so correspond to the 

 dorsal frUls of the Rhizostomae multicrispai (Pilemidce and Crambessidce, comp. my 

 System, pp. 464, 581). Of the three narrow wings of the triangularly pyramidal terminal 

 knobs, one also lies axially, and the other two abaxially ; they are the terminal processes 

 of the three frills, but they have lost their funnel frills, and look as if they had been 

 ground down. The numerous and irregular oral openings on and between the folds of 

 the frills are sometimes cleft-shaped, sometimes funnel-shaped ; the margins of these 

 funnel frdls, which were formerly called sucking-mouths, are thickly beset with 

 numerous microscopic small oral tentacles or digitella. Here in Leonura, as in all other 

 Rhizostoma, there are " prolonged urticating papillae of the ectoderm," solid cylindrical 

 processes of the gelatinous substance of the arm, whose ectodermal epithelium partly 

 forms thread cells, partly epithelial muscular cells (comp. Otto Hamann, Die Mundarme 

 der Rhizostomen und ihre Anhangs-Organe ; Jena. Zeitschr. fur Naturw., Bd. xv. 1881). 

 The gastrovascular system (figs. 2, 4-8) of Leonura is almost completely homologous 

 with that of the closely-allied Leptobraehia, and also in many respects with that of 

 Crambessa, of which Grenadier and Noll (1876) have given a description which is very 

 accurate and true to nature (comp. my System, 1879, p. 616, taf. xxxviii.-xl.). As in all 

 Acraspedse, we can distinguish the central principal intestine from the peripheric coronal 

 intestine. The central principal intestine consists of the large cruciform central stomach 

 and of the smaller buccal stomach connected with it by the four pillar canals and the 

 vascular system of the arms, which runs out from the latter. The central stomach (figs. 

 2, 4, gc) has the cruciform shape and extent of the gastrogenital membrane afready 

 described (gg), which forms its lower wall ; the upper wall is formed by the smooth 

 endodermal surface of the central gelatinous umbrella disk. The sixteen radial canals 

 composing the peripheric coronal intestine run towards the outside on the peripheric 

 margin of the central stomach {gin), where its upper and wider walls touch, whdst, at the 

 same time, the four perradial pillar canals (" canales pilastrales," ctl) pass downwards. 

 The latter spring from the distal ends of the four cross limbs of the central stomach, 

 immediately below the starting point of the four perradial subunibral canals, run from 

 above and outside, below and inside on the axial inner side of the four arm pillars, and 

 these open into the buccal stomach (ga). We shall apply this name to the small 



