332 EVENINGS AT THE MICROSCOPE. 



there is a very manifest tendency to a fibrous character in 

 its texture, the fibres being directed from the exterior to- 

 wards the interior, supposing the lobes to have their points 

 in contact. 



Let us now look at the margin of the disk. Here are 

 attached twenty-four slender tentacles, six in each quad- 

 rant formed by the divergent ribs, or radiating canals. 

 Each tentacle springs from a thickened bulb, which is 

 imbedded in the margin of the disk ; it is evidently 

 tubular, but the tube is not wider in the bulb than in the 

 filament. The general surface is rough with projecting 

 points, which in some assume a very regular spinous ap- 

 pearance, and the tentacle terminates in a blunt point. 

 The discal part of the bulb is fringed with a row of minute 

 bead-like spherules. Around the edge of the circumference 

 of the disk, on the exterior, are arranged eight beautiful 

 and conspicuous vesicles or organs for hearing. They are 

 placed in pairs, those of each pair being approximate, and 

 appropriated to each of the quadrants of the circle. Each 

 of these organs consists of a transparent globe, not enve- 

 loped in the substance of the disk, but so free as to appear 

 barely in contact with it : it contains a single otolithe, of 

 high refractive power, placed, not in the centre, but towards 

 the outer side. The inexperienced naturalist, on first 

 seeing these organs, would unhesitatingly pronounce them 

 eyes, and the otolithe, or ear-stone,* the crystalline lens. 

 They are, however, pretty certainly, rudimentary organs of 

 hearing ; the crystalline globule or otolithe being capable 

 of vibration within its vesicle. Their exact counterparts 

 are found in many of the smaller Medusae,, as we lately 

 saw in the Thaumantias. 



The disk is endowed with an energetic power of con- 

 traction, by which the margin is diminished, exactly like 

 that of a Medusa swimming ; and the tentacles have also 

 the power of individual motion, though in general this is 

 * See note on page 56. 



