STRUCTUKE OF THE MEDUS.E. 21 



Drs. Hertwig made no observations on the peri- 

 pheral nervous system of the covered-eyed Meckisse ; 

 but they do not doubt that such a system would 

 admit of being demonstrated, and intliis 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 Schiifer, F.R.S., conducted in my 

 laborator}^ a careful research upon the histology 

 of tlie Medusae, 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 Avay, so to 

 speak, towards becoming fully diff'erentiated 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 

 Medusce, 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 Medusae 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," 

 Fhil. Trans., pt. ii., 1878. 

 3 



