STRUCTURE OF THE MEDUSZ. 21 
Drs. Hertwig made no observations on the peri- 
pheral nervous system of the covered-eyed Medusz ; 
but they do not doubt that such a system would 
admit of being demonstrated, and in this connection 
they cite the observations of Claus, who describes 
numerous ganglion-cells as occurring in the sub- 
umbrella of Chrysaora. Here I may appropriately 
state that before Drs. Hertwig had published their 
results, Professor Schafer, F.R.S., conducted in my 
laboratory a careful research: upon the histology 
of the Medusz, and succeeded in showing an 
intricate plexus of cells and fibres overspreading 
the sub-umbrella tissue of another covered-eyed 
Medusa (Aurelia aurita).* He also found that 
the marginal bodies present a peculiar modification 
of epithelium tissue, which is on its way, so to 
speak, towards becoming fully differentiated into 
ganglionic cells. 
Lastly, returning to the researches of Drs. Hert- 
wig, these authors compare the nervous system 
of the naked-eyed with that of the covered-eyed 
‘ Medusze, with the view of indicating the points 
which show the latter to be less developed than 
the former. These points are, that in the nerve- 
centres of the covered-eyed Medusz there are no 
true ganglion-cells, or only very few; that the 
mass of the central nervous system is very small; 
and that the centralization of the nervous system 
is less complete in the one group than in the other. 
In their memoir these authors further supply much 
* See ‘‘ Observations on the Nervous System of Aurelia aurita,”’ 
Phil. Trans., pt. ii., 1878. 
