320 



EVENINGS AT THE MICROSCOPE. 



are a good many more, far more minute, without any 

 bulbs ; — from four to seven between every two of the 

 primary ones. We won't mind these, but, bringing the 

 margin itself into focus, and moving it along the stage 

 horizontally, we presently see one and another singular 

 organs. They are eight in all, two being placed, but irre- 

 gularly, in each of the four quadrants of the circle formed 

 by the radiating canals. 



These are organs of hearing, very closely similar to 

 those which we see imbedded in the bosom of the Snail 

 and other Mollusca. Here they are comparatively large, 

 and unusually well furnished. Each is a semi-oval en- 

 largement of the flesh of the margin, in close connexion 

 with the walls of the marginal canal, hollowed so as to in- 

 close a capacious cavity, in which are placed a considerable 

 number, — from thirty to fifty in this individual — of oto- 

 lithes, or spheres of solid, transparent, highly refractive 



OTOLITHEB OP THATJMANTIAB. 



substance. They are arranged in a double line, forming a 

 crescent, and those which are nearest the centre are larger 

 than those towards the extremities of the line. I believe 

 some observers have seen oscillatory and rotatory move- 

 ments among these spherules, as in the Mollusca ; but I 

 have invariably found them motionless in all the species of 

 Medusa that I have examined, as you see them here. 

 One more little beauty from our stock, and we have 



