74 



The morning of the 13th of June, in 34° 33' la- 

 titude, we saw large masses of this last mollusca 

 in it's passage, the sea being perfectly calm. We 

 observed during the night, that, of three species 

 of medusas which we collected, none yielded any 

 light but at the moment of a very slight shock. 

 This property does not belong exclusively to the 

 medusa noctiluca, which Forskssl has described 

 in his Fauna i^Egyptiaca, and which Gmelin has 

 applied to the medusa pelagica of Lcefling, not- 

 withstanding it's red tentacula, and the brownish 

 tuberosities of it's body. If we place a very irri- 

 table medusa on a pewter plate, and strike 

 against the plate with any sort of metal, the 

 small vibrations of the plate are sufficient to 

 make this animal emit light. Sometimes in gal- 

 vanising the medusa, the phosphorescence ap- 

 pears at the moment that the chain closes, though 

 the exciters are not in immediate contact with 

 the organs of the animal. The fingers with 

 which we touch it remain luminous for two or 

 three minutes, as is observed in breaking the 

 shell of the pholades. If we rub wood with the 

 body of a medusa, and the part rubbed ceases 

 shining, the phosphorescence returns if we pass a 

 dry hand over the wood. When the light is ex- 

 tinguished a second time, it can no longer be re- 

 produced, though the place rubbed be still hu- 

 mid and viscous. In what manner ought we to 

 consider the effect of the friction, or that of the 



