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



the umbrella margin along with the most important part of the muscular and nervous 

 systems (sense organs and tentacles) the umbrella corona (" corona umbralis "). These 

 two principal sections of the umbrella correspond at the same time to the two principal 

 sections of the gastrovascular system, as the central principal intestine is situated in 

 the umbrella disk, but the peripheric coronal intestine in the umbrella corona. The 

 boundary between the disk and the corona is often sharply defined externally, as an 

 exumbral coronal furrow (" fossa coronaris ") is inserted more or less deeply between the 

 two, as in many Narcomedusae (Pis. IX.-XIL), Peromedusas (PI. XVIIL), Cuboinedusse (PI. 

 XXVI.), and in a few Discornedusse, very distinctly in many Cannostomaa (Pis. XXVIL- 

 XXIX.). The central umbrella disk is more discoid or lens shaped (" umbrella lens," 

 " lens umbralis") in the depressed Medusa}, but more conical or bell shaped (" umbrella 

 cone " " conus umbralis ") in the higher vaulted Medusae. In the Craspedotas the 

 peripheric umbrella corona ends in the typical velum of this section, but in the 

 Acraspecla3 in the characteristic lobe corona or velarium. 



§64. Umbrella peduncle and umbrella cupola ("pedunculus umbralis" and " cupola 

 umbrellse "). In many Medusa?, though only in the minority, the " apex of the umbrella " 

 (the uppermost, aboral and proximal part of the " notumbrella ") is not arched and 

 rounded as usual, but prolonged into a projecting apical process or a conical, peduncle- 

 like process. In one order only, the Stauromedusse, it is developed into a true umbrella 

 peduncle (" pedunculus umbrellse "), whose aboral end, the " foot plate," serves for adhesion 

 to the bottom of the sea or to foreign bodies (Pis. XVI., XVII. ; System, taf. xxi., xxii.). 

 But in many other Medusae of different orders (namely, of Anthomedusae and Peromedusse) 

 in place of an apical peduncle we find a peculiar umbrella cupola or conical apical 

 process (" cupola umbrellas ") at the top of the umbrella. This is the ecpiivalent of the 

 adhering peduncle, and contains, like it, a caecal axial "apical canal" or "peduncle 

 canal" (Tesserantha, PI. XV. figs. 1-3, p). A special morphological interest attaches 

 itself to these parts in that they are heirlooms from the polyp ancestors of the Medusse, 

 and are homologous with the peduncle and peduncle canal of the polyps, by means of 

 which the latter are fastened to the bottom of the sea. 



§ 65. Gastral peduncle and gastral cone (" pedunculus gastralis " and " conus gastralis "). 

 An oral process is often found, though only in the Craspedotae, on the concave inner 

 surface of the central umbrella disk, in the same way as the umbrella peduncle or the 

 umbrella cupola is developed from it as an aboral process. This oral process first appears 

 as a flat, insignificant, conical elevation in the centre of the endodermal hollow surface 

 of the " notumbrella," and projects, more or less, into the central gastral cavity (System, 

 taf. xi. xiv. xv.). By further growth from this gastral cone, a long cylindrical 

 gelatinous peduncle is developed, which projects far into the umbrella cavity or even 

 beyond the umbrella opening, and which takes the surrounding parts of the " coel- 

 umbrella" along with it. The gastral sac lies no longer, as usual, in the bottom of the 



