If) JELLY-FISH, 



Medus?e, we have a most important step in. the 

 histology of these animals. Haeckel's results in 

 these respects have since been confirmed by Clans, 

 "Grundziige der Zoologie," 1872; Allman, "A 

 Monograph of the Gymnoblastic or Tabularian 

 Hydroids," 1871 ; Harting, " Notices Zoologiques," 

 Niedlandisches "Archiv. f ZooL," bd. ii., Heft 3, 

 1873 ; F. E. Schulze, " Ueber den Ban von Syncorzne 

 Sarsii " ; 0. and R. Hertwig, " Das Nervensystem 

 und die Sinnesorgane der Medusen." 



The last-named monograph is much the most 

 important that has appeared upon the histology of 

 the Medusa?. I shall, therefore, give a condensed 

 epitome of the leading results which it has estab- 

 lished. 



There is so great a difference between the nervous 

 system of the naked and of the covered eyed 

 Medusse, that a simultaneous description of the 

 nervous system in both groups is not by these 

 authors considered practicable. Beginning, there- 

 fore, with the naked-eyed division, they describe 

 the nervous system as here consisting of two parts, 

 a central and a peripheral. The central part is 

 localized in the margin of the swimming-bell, and 

 there forms a " nerve-ring," which is divided by the 

 insertion of the " veil " * into an upper and a lower 

 nerve-ring. In many species the upper nerve-ring 

 is spread out in the form of a flattish layer, which 



* This is the name given to a small annular sheet of tissue 

 which forms a kind of floor to the orifice of the swimming-bell, 

 through the central opening of which floor the manubrium passes, 

 The structure is shown in Fig. 1. 



