LUMINOSITY OF THE MEDUSA. 59 



If, says Spallanzani, in the beginning of the night 

 we enter the Strait of Messina [October was the 

 month in which these observations were made] in 

 a low bark or boat, coasting near the land, where 

 the water is perfectly calm, the Medusae, usually very 

 numerous, there begin to shine with a light which, 

 as the darkness increases, acquires intensity and ex- 

 tent, every Medusa resembling a bright torch, that 

 may be seen for some hundreds of paces round, and 

 on approaching it the brilliant phosphorescence shows 

 distinctly the form of the creature's body. This light, 

 when the evening twilight is extinct, is of a lively 

 white, which strikes the eye even when the animal is 

 five-and-thirty feet below the surface. As the Medusa 

 by its oscillation transfers itself from place to place, 

 so the light is variable. Sometimes it continues for 

 a quarter of an hour, half an hour, or more; but at 

 other times, it suddenly becomes extinguished, and 

 does not reappear till after a considerable interval. 



We are indebted to Spallanzani for a great number 

 of curious experiments upon this part of their history. 

 That careful observer ascertained that the power of 

 emitting light seems to be limited to the targe arms, 

 or tentacles, the muscular zone of the umbrella-like 

 disc, and the stomachal cavity, the rest of the animal 

 only shining by transmitted light. He then endea- 

 voured to find out the cause of this phosphorescent 

 appearance, and ascertained that it is owing to the 

 secretion of a peculiar glutinous fluid which exudes 

 from the surface of the organs above mentioned. 

 This secretion, even when mingled with other fluids, 

 communicates to them a degree of phosphorescent 



