REPORT ON THE DEEP-SEA MEDUSAE. xlvii 



the first two orders of the four orders of this section, the Stauromedusse and Pero- 

 Medusae, is next to unknown ; the two other orders seem to comport themselves in some- 

 what different ways. The Cubomedusse (Charybdeidse""aiid Chirodropidae, PL XXVI. figs. 

 25, 26) are distinguished by a strong simple subumbral nerve ring which runs above the 

 umbrella margin at a considerable distance from it. It lies embedded in a groove of the 

 subumbrella, whose muscular plate is interrupted by it, and consists of a clear axial 

 cord, two turbid cords of fibrillae (an upper and an under) lying on the former and a 

 peculiar overlying nerve epithelium. The nerve ring is swollen at eight places into eight 

 ganglia. The four perradial ganglia are larger and lie higher at the bases of the four 

 highly developed sense clubs ; they send out sensible nerves to the sense clubs and motor 

 nerves to the muscular plate of the subumbrella. The four interradial ganglia he deeper at 

 the basis of the four strong tentacle pedalia, and send out both sensible and motor nerves 

 to the umbrella margin and the tentacles. Wide-spread plexus of fibrillae, in which numer- 

 ous multipolar and fusiform ganglion cells are situated, he in the subumbrella and the 

 velarium, and are connected with the nerve ring and its eight ganglia. The nervous system 

 of the allied Peromedusae, where we may expect to find the nerve ring in the depth of 

 the exumbral coronal furrow or at the coronal muscle, is probably of the same nature as 

 that of the Cubomedusae. On the other hand, the" nervous system of the Discomedusae, 

 which has been often examined, varies in its nature in so far that the nerve ring retreats 

 whilst the principal sense clubs (four perradial and four interradial) appear in the fore- 

 ground as eight separate marginal nerve centres. Each of these eight sense clubs or 

 marginal bodies in the Discomedusae contains in itself the organs of sense described 

 below, and its base encloses an independent nerve centre, which here, and as in the 

 Cubomedusaa, may be termed the principal ganglion. This consists of a thick pad of 

 nerve fibrillae and ganglion cells, which are in iumiediate connection both with the under- 

 lying tactile cells of the ectodermal sense epithelium and with the remaining organs of 

 sense of the rhopalium. Other filaments connect it with the nervous plexus of the 

 subumbrella, which extends between the ectodermal epithelium and the muscular plate 

 of the latter, and contains large motor ganglion cells. The bundles of fibrillar which 

 form immediate connection between the eight principal ganglia of the rhopalia and 

 correspond to the strong nerve ring of the Cubomedusae may be looked for in the 

 Discomedusae in the bottom of the umbrella cavity. 



§ 75. Organs of sense (" sensillae "). All Medusae possess organs of sense on the um- 

 brella margin. The umbrella margin itself is covered for the most part with sense epithe- 

 lium ; it is the mother-ground and place of origin of different sensillae. These appear in the 

 simplest (and almost universally spread) form as tentacles, which are plainly homologous 

 to the margin tentacles of the polyps from which they have originated phylogenetically. 

 The sensillae are represented only by tentacles in few groups of Medusas. In most groups 

 besides tentacles we find differentiated organs of sense on the umbrella margin, which 



