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



pletely covered with parts of the thin-membraned lamellae of the septa, hanging in tatters, 

 and with the reproductive organs and mesenteric filaments. The latter protruded partly 

 from the oesophagus, partly from rents and fissures in the oral disk and wall, and partly 

 from the openings, which replace the tentacles and represent them morphologically. 



After the tattered fragments had been partially removed, it was found that one side 

 of the Actinia was formed by the oesophagus and oral disk, the other by the wall and the 

 pedal disk (fig. 3). The pedal disk is only slightly distinguished from the wall as a shallow 

 depression 1*5 cm. in diameter, the bottom of which forms a convex projection into the 

 interior of the gastric space of the Actinia. The wall, which is about 27 cm. long, shows 

 distinct longitudinal furrows, which run from the margin of the pedal disk to the margin 

 of the oral disk, and indicate externally the origins of the septa. As they amount to more 

 than seventy in number, they correspond to thirty-six pairs of septa, which were also 

 visible on dissection. Small knobs, which may perhaps be compared to the " bourses 

 marginales" of other Actiniae, lie one in each of the interspaces between these longitudinal 

 lines, at a little distance from the margin of the oral disk. The surface of the wall is 

 otherwise qnite smooth. 



The endodermal circular layer of fibres is pleated as far as the wall extends, and rises 

 in muscular folds, which usually remain simple or are only slightly branched (fig. 10). 

 The folds are more extensively branched only in the uppermost section of the body, 

 where they form a sphincter which lies between the marginal spherules and the corona of 

 stomidia, somewhat below the latter, and causes the wall to project outwardly (fig. 8). 

 A longitudinal section through the wall, therefore, shows us two evaginations lying at the 

 upper end, the one above the other, in which the supporting lamella becomes very much 

 thinner. The lower one is caused by the marginal spherule, the upper by the circular 

 muscle ; the former contains a hollow space and is lined by a weak muscular layer, 

 the interior of the latter is almost completely filled by the deep muscular folds, 

 whose arrangement is more minutely given in fig. 9. The ramification of the separate 

 folds decreases both above and below, so that the circular muscle is gradually transformed 

 into the usual muscular layer. 



The entire absence of the tentacles is a striking feature of the oral disk ; they are 

 replaced by openings like buttonholes (fig. 6), which I shall term " stomidia," and on 

 account of which I have named the genus PoJystomidiicm. Their exact number coidd not 

 be directly determined, as the oral disk was greatly injured in many places, but, bearing 

 in mind their relation to the septa, it may be estimated at about seventy-two. In 

 dissecting the septa we find that one stomidium opens into each radial chamber. The 

 stomidia belonging to the intraseptal spaces are usually smaller, and form an inner circle 

 by themselves ; the stomidia of the interseptal spaces alternate with them, and are placed 

 in an outer circle ; their longitudinal diameter runs in a radial direction, and amounts to 

 about 0'5 cm. 



