4O Instinct and Intelligence 



cular fibres surround the manubrium and extend 

 outwards over the inner surface of the bell ; they 

 may be followed into the velum, which is essen- 

 tially a muscular structure. 



We find, in connection with the ectoderm of 

 the under surface of the bell and its muscular 

 fibres, a complex arrangement of nerve cells and 

 fibres. (Fig. 4.) Mr. G. J. Romanes compares 

 the network of nerve fibres 

 of the inner subectodermic 

 layer of a Medusoid's bell 

 with a " disc of muslin, the 

 fibres and meshes of which 

 are finer than the closest 

 cobweb." 1 



The nerve cells originate, 

 as in Hydra, p. 36, from 

 the sensitive protoplasmic 

 substance of the outer layer (ectoderm) of cells 

 forming the margin, and under-surface of the 

 bell. In some Medusoids a double circle of 

 nerve cells and fibres extends round the struc- 

 tures constituting the margin of the bell ; from 

 these nerve cells numerous fibres are given off 



J. Romanes on Jelly-fish, Star-fish, .and Sea-Urchins, 



FIG. 4. 



pp. 



G. 



'7. 



