REPORT ON THE DEEP-SEA MEDUSAE. xxiii 



the principal radii, on account of their prominent morphological significance, radii of 

 Orders III. and IV. belong, on the other hand, to the succursal or secondary radii, which 

 can only claim a subordinate value as compared with the others. In most Craspedotae the 

 eight adradii are of no special value; they are often without organs, or only bear the eight 

 tentacles of Order III. They are distinguished only in the vesiculated Leptomedusae 

 (Eucopidse and iEquoridas), as the eight typical " velar marginal vesicles " of this group 

 lie in them (fig. C, ov, System, taf. xi., xiii.). The eight adradii are of much greater 

 importance in the Acraspedaa. In these the eight hollow marginal " arms " of the 

 Lucernaridae and the homologous eight oral lobes of the Pericolpidae lie in the eight 

 adradii, also the eight marginal pouches of the Charybdeidas and the eight tentacles of 

 the Ephyra. 



§ 35. Subradii, or transverse radii of Order IV. The sixteen subradii lie in all quadri- 

 partite Medusae in the middle between the eight adradii on the one side and the eight 

 principal radii (four perradii and four interradii) on the other; thirty -two angles of ll£ 

 degrees remain between the former and the latter. Contrasted with the positive signi- 

 ficance of the principal radii, which in all Medusas mark the active meridian planes of 

 development, and the regular positions of the most important organs, the subradii have, 

 at most, a completely negative value ; they mark those meridian planes of the body which 

 of all comport themselves the most passively and indifferently. In most Craspedotae no 

 special organs lie in them, excepting in some Narcomedusae, as, for example, in AUginura 

 (Pis. XIII., XIV.), where the sixteen internemal pouches (with the genitalia) and at the same 

 time the sixteen auditory clubs of the umbrella margin lie subradially. In the majority 

 of the Acraspedae, the sixteen subradial planes are distinguished by the absence of ab 1 

 organs. In a few groups of this section only they mark the site of isolated marginal 

 organs. For example, the sixteen marginal lobes of the Periphyllidae, among the Pero- 

 medusae (Pis. XVIII. , XIX.), and of the Ephyridae, among the Discomedusae (woodcut, 

 fig. A, I) lie subradially. The latter are so far of importance that the marginal lobes 

 of all Discomedusae have arisen from them : indeed, it is advantageous for the more 

 accurate morphology of this division to distinguish two groups among the sixteen 

 subradial " Ephyra lobes " ; the eight Ephyra lobes, enclosed in pairs by the perradii, are 

 corradial, whilst those enclosed in pairs by the interradii are exradial. 



§ 36. Umbrella disk and umbrella corona (" discus umbrellae" and " corona umbrellae "). 

 In all Medusae the most important groups of organs of the body are divided in such a ■ 

 way that a certain regularity seems common to them all. We can recognise especially 

 in distinct contrast two principal parts of the body between the central umbrella disk 

 (" discus umbralis ") and the peripheric umbrella corona ; the former contains the larger 

 and most important part of the vegetative organs, the latter, on the contrary, the prepon- 

 derating and most important part of the animal organs. The stomach and mouth, as well 

 as the many important organs developed round the mouth (oral lobes, or d arms, &c), 



