4 THE VOYAGE OF H.M.S CHALLENGER. 



grooves on both sides of the midrib divide the genitalium into the same number of lobes, 

 it assumes the form of a delicate pinnated leaf. Its five to six pairs of pinnules become 

 longer from the top to the bottom and are delicately notched at the edges like many 

 fern-fronds (fig. 6). Numerous large and small ova appear lying very closely together 

 on the upper surface of the single pinnated leaves. The ova are large, naked amoeboid 

 cells, of irregular roundish or polyhedral outline, which enclose a large clear germinal 

 vesicle. In this nucleus a dark germinal spot of considerable size (nucleolus) is visible 

 which contains a distinct nucleolinus (fig. 8). The four reproductive leaves occupy 

 the greater part of the thickened wall of the central stomach, so that only four narrow 

 interradial area? of its external surface are free from them (fig. 3). More minute 

 investigation, however, shows that only the perradial midrib and the aboral basal 

 parts of the reproductive leaves are integrate portions of the wall of the stomach itself, 

 from the ectoderm of whose angles they are developed. On the other hand, the oral 

 points of the genitalia and the larger part of their lateral margins are free, and only 

 lie superficially on the external wall of the stomach. Between the colourless ova, 

 as in the remaining parts of the wall of the stomach and of the umbrella margin, 

 there are numerous fine granules of the same blood-red pigment (insoluble in spirit 

 of wine) which causes the red colour of the oral styles and of the stinging capsules of 

 the tentacles. 



The oral styles (" stomostyli," figs. 1-5). In this species, as in several other Margelida? 

 {Hippocrene, Nemopsis, Bathkea, Limnorea, Sec), the characteristic oral styles form 

 extremely delicate multi-branched bunches, distinguished by their blood- red colour. These 

 branches are, however, more numerously and more strongly developed here in proportion to 

 the rest of the body than in all the other Margelidse. When fully extended (as it appears in 

 the particular specimen before us) they occupy a space exceeding that of the whole umbrella. 

 The four perradial strong stems of the oral styles are nearly as thick as the swollen basal 

 pieces of the tentacles and spring from the truncated point of the central stomach round 

 about the basis of the long oesophagus almost at the height of the plane of the velum 

 (fig. 1). Each of the four strong stems divides directly into two thick principal branches, 

 which again bifurcate after a short course. These branches appear to dichotomise at least 

 six or eight times (sometimes oftener), so that the aggregate number of the terminal 

 branches amounts to more than a thousand. The calibre of the branches becomes smaller 

 with each new bifurcation, so that the four basal principal stems are at least six to eight 

 times as thick as their terminal branchlets. Each of the latter ends with a spherical 

 stinging knob, which is composed of numerous longitudinally extended, radially placed 

 thread cells, and bears long fine cnidocils (fig. 5 «). The minute structure of the 

 oral styles and their branches is the same as in other Margelicke. Their principal mass 

 forms an endodermal cellular axis, consisting of a single row of flat coin-shaped endoderm 

 cells placed in series like a rouleau of money. Their nuclei, surrounded by an area of 



