Phosphorescent Animals. 71 



pass through fine gauze ; yet many were distinctly 

 visible by the naked eye. The water, when placed 

 in a tumbler and agitated, gave out sparks, but a 

 small portion in a watch-glass scarcely ever was 

 luminous. Ehrenberg states that these particles all 

 retain a certain degree of irritability. My observa- 

 tions, some of which were made directly after taking 

 up the water, gave a different result. I may also 

 mention that, having used the net during one night, 

 I allowed it to become partially dry, and having 

 occasion twelve hours afterwards to employ it again, 

 I found the whole surface sparkled as brightly as 

 when first taken out of the water. It does not 

 appear probable, in this case, that the particles could 

 have remained' so long alive. On one occasion, 

 having kept a jelly-fish of the genus Diancea till it 

 was dead, the water in which it was placed became 

 luminous." 



Since Darwin made his famous trip scores of ani- 

 mals have been added to the list of those which emit 

 light, yet the true secret of the illumination has not 

 yet been determined. 



