

MOLLUSCA. 307 



tained was agitated, their body instantly became one 

 blaze of phosphoric light, which, upon close examina- 

 tion,, could be observed to proceed from myriads of 

 luminous dots, occupying the situations of the small 

 brown specks noticeable in the fleshy structure of the 

 mollusc. Upon the irritating cause * being removed, 

 the phosphoric light gradually expired, and the Pyro- 

 some remained in darkness until again disturbed, when 

 it once more illuminated surrounding objects with its 

 vivid gleam; and this was repeated until after the 

 death of the animal, when no luminous effect could be 

 reproduced. When living specimens were immersed 

 in fresh water, they not only existed for some hours 

 but emitted a constant light : even after they had been 

 so much enfeebled as to cease to give light in sea- 

 water, or after they had been seriously mutilated, their 

 phosphorescence invariably reappeared when they were 

 put into fresh water, which appears to act as a peculiar 

 stimulus in reproducing the phosphoric light of these, 

 as well as of most other marine luminous animals. 



The Pyrosome does not communicate its luminosity 

 to water, nor to any object in contact with it, (like many 

 luminous medusa,) its body being enveloped in a mem- 

 brane that has no luminous secretion. But when the 

 mollusc is cut open in water, some of the brown specks, 

 before-mentioned, will escape, and diffusing themselves 

 through the fluid, shine independent of the animal : in 

 this respect, as well as in their structure and colour, 

 bearing some resemblance to the luminous scale on the 

 abdomen of the small fire-fly of Bengal. When this 

 mollusc is first removed from the sea, the orifice, or 

 mouth, at one extremity of its body is nearly as wide 



* Friction is not the only cause of the Pyrosome emitting its light ; 

 for the slightest touch on one part of its body is sufficient to illumi- 

 nate the whole. 



x 2 



