196 POPULAR HISTORY OF THE AQUARIUM. 



are luminous. But since this TTork is not undertaken for 

 the purpose of settling doubtful affinities, I must leave this 

 question with a confession of incompetence. My object is 

 rather to collect and to present to my readers the results of 

 observations made on water-animals imprisoned for the pur- 

 pose in vessels of their native element. 



How many of the Infusoria may yet turn out to be lumi- 

 nous we do not know, but many of the Annelids, Medusae, 

 and fishes are known to be so. Dr. Baird gives an account 

 of luminous appearances occasioned by Entomostraca. He 

 tells us of " the broad bright flash, \dvid enough to illumi- 

 nate the sea for some distance round, while the most splen- 

 did globes of fire were seen wheeling and careering in the 

 midst of it, and by their brilliancy outshining the general 

 light." Dr. Baird drew a bucketfull of water, and " allowed 

 it to remain quiet for some time, when upon looking into it in 

 a dark place, each animal could be seen distinctly emitting 

 a bright speck of light. Sometimes this was like a sudden 

 flash, at others appearing like an oblong or round lumi- 

 nous point, which continued bright for a short time, like a 

 lamp lit beneath the water, and moving through it, still pos- 

 sessing its definite shape, and then suddenly disappearing. 

 When the bucket was sharply struck on the outside, there 



