20 BRITISH HYDROID ZOOPHYTES. 



them. To tliese organs the power of si^i^ht is 

 attributed. In addition, along the margin 

 of the bell there occur other organs which 

 have more the appearance of eyes, very 

 prominent and staring in character. 



Lithocysts, organs of direction. 

 These are little globular sacks containing a 

 calcareous spherule, and are termed lithocysts. 

 It was formerly thought that they might have 

 been organs of hearing, but they are now 

 regarded as organs of the sense of direction, in 

 steering a course. 



Nerves and Muscles. With regard to 

 the nervous and muscular systems entailed by 

 the development of the ** bell " for swimming 

 purposes. Romanes, in his work on " Jelly 

 Fish, Starfish and Sea Urchins," gives an 

 interesting account of experiments in 

 dissection which he carried out on the 

 Hydromeduste, pointing conclusively to a 

 differentiation of tissue in the direction of 

 nerves and muscles. 



Two rings of nerves. It is now, 

 however, established, that tlierc^ exists arouml 

 the margin of the bell, two rings of neives and 

 nerve cells, one ring occurring just above and 

 the other just below the " veil " process. 



