SCYPHOMEDUS.E MAESUPIALIDA. 



250 



modified. As in Lucernaridce, the vascular spaces are wide pouches 

 divided from each other by four narrow septa (figs. 198, 199). 



The nervous system is allied to that of the Hydromedusce by the 

 presence of a sharply defined nerve-ring. This nerve-ring is placed 

 on the sub-umbrella side of the bell, and, since at the bases of the 

 four sense organs it lies further from the margin than it does at the 

 corners of the bell, it has a sharply marked, zig-zag course. The 

 nerve fibrillae given off from it mostly supply the muscular system of 

 the sub-umbrella, and there give rise to numerous reticula of fibrillse 

 connected with large ganglion cells. Large bundles of fibrillse com- 

 parable to nerves have only been found in the four radii of the mar- 

 ginal bodies. The latter attain a high degree of development, since 

 the knob-like swelling in which they terminate possesses, in addition 

 to the lithocyst, a complicated visual apparatus consisting of two 

 large unpaired median eyes and four 

 small paired lateral eyes. 



The generative organs have a very 

 peculiar form. They are separated 

 from the gastric filaments and as 

 thin, rather broad plates attached in 

 pairs to the four partition walls, 

 reach the whole length of the 

 vascular pouches. Unfortunately 

 nothing is as yet known of the 

 development. 



Fam. Charybdeidee. CUavyldea mar- 

 x it j) -I alls Per. Les. (Marsupialis Planci 

 Les.) Mediterranean. 



(3) Sub-order : Discophora (Acra- 

 speda), Ephyra-medusce. 



Disc-shaped Acalepha, the margin of whose disc is divided into eight 

 .lobes. They have at least eight sub-marginal sense organs contained in 

 niches, and with the same number of ocular lobes. As a rule there are 

 four great cavities in the umbrella for the generative organs. 



The Discophora, which are generally known simply as Acalepha, 

 can at once be distinguished from the Calycozoa and the Charybdeidee 

 by the disc-shaped lobed umbrella and usually by the large size of 

 the oral tentacles. The lobes of the umbrella, however much they 

 may differ in detail, can always be reduced to the eight pairs of 

 lobes of the Ephyra, which, as the common starting-point of the 

 Discophora, presents most clearly the eight-rayed symmetry char- 



Fre. 199. The apicalhalf of a Charyldea 

 divided transversely, seen from the 

 sub-umbrella side. The four oral 

 arms are visible. Ov, Ovaries on the 

 four septa, S; Ost, ostia of the gas- 

 trie pouches ; Gf, gastric filaments. 



