5G4 
PROFESSOR E. A. SCHAFER ON THE 
The nervous system of Aurelia consists (1) of the marginal bodies or lithocysts, the 
discharging function of which has been clearly demonstrated by Mr. Romanes ; (2) of 
certain tracts of peculiarly modified epithelium in their vicinity, which we may term 
the nerve-epithelium ; (3) of an interlacement of nerve-fibres, which covers the whole 
of the under surface of the muscular sheet, lying between the muscular fibres and the 
ectoderm-cells, and partly amongst the latter, and which may be termed the sub- 
umbrellar plexus. 
Subumbrellar Nervous Plexus. 
The plexus can be distinctly seen even in the fresh tissue if care be taken to bring 
the subumbrella fiat and uninjured under microscopic observation, and the fibres then 
have very much the appearance of the sympathetic fibres, or fibres of Ilemak, of the 
Vertebrata, and, like these, show an indistinct longitudinal striation. Here and there 
oval or fusiform swellings occur in the course of the fibres, and in the larger of the 
swellings a vesicular nucleus, and a distinct bright nucleolus may be detected. These 
appearances are so obvious as to allow of no question that we have before us undoubted 
nerve-fibres, and bipolar ganglion-cells. The tissue which they underlie being just as 
clearly muscular, with well-characterised cross-stake, it is interesting to observe, even 
so low down in the metazoic scale as the Medusae, that the textures, which in the 
higher animals are generally looked upon as the most highly differentiated, should 
have already attained a degree of structural complexity and of functional activity in 
many respects scarcely inferior to the nervous and muscular tissues of Vertebrates. 
The subumbrellar nerves. Structure of the nerve-fibres. — The reagents which are 
ordinarily employed for the demonstration of nervous tissues, and especially the chloride 
of gold, bring the structures in question to view in the most striking manner possible. 
As in the higher animals, the nerve-fibres and the substance of the ganglion-cells 
become stained of a deep violet colour by this reagent, so that the fibres may be 
followed with ease over large tracts of the surface (Plate 50, figs. 1-7 ; Plate 51, 
figs. 11-16). Osmic acid preparations lack this distinctiveness of colouration, so that 
the nerves are scarcely better exhibited in situ than in the fresh preparation. But 
whereas after treatment by the chloride of gold method the fibres appear markedly 
smaller than in the fresh tissue, and seem to have become somewhat shrunken, in the 
preparations made with osmic acid they preserve their original size and for the most 
part their pristine appearance (Plate 50, fig. 8). If the nerve-fibres which have been 
stained with chloride of gold be attentively observed, it may be seen that they are 
surrounded by a clear space which separates them from the tissue in which they lie. 
This space may have been produced by the expression of fluid from the fibre during 
its supposed shrinkage, or on the other hand it may represent a previously existing 
homogeneous sheath, surrounding an axis-cylinder ; and, if this were the case, certain 
small nuclei, which are occasionally seen adhering to the fibres (figs. 13 and 14, n.), 
