420 FISHES 



except once when the fish was pressed against the side of the 

 aquarium, and a scarcely perceptible glow was observed. The 

 fish lives on the shore, and is quite common, so that if it was 

 phosphorescent in its natural state, the fact could scarcely fail 

 to attract notice, but no evidence of light being observed to be 

 emitted by the fish has ever been brought forward. On the 

 other hand, it is certain that the organs are really light-produc- 

 ing organs, for when the fish was put into sea-water to which 

 a little ammonia had been added, it exhibited a most brilliant 

 glow of light along the lines where the organs were situated, 

 and the individual organs were distinguishable as the sources of 

 the light. The light appeared after five minutes, remained 

 bright for a few minutes, and during twenty minutes gradually 

 diminished almost to zero. Rubbing the hand over the organs 

 was always followed by a distinct increase in the luminosity. 

 Even pieces of the skin containing the organs cut from the 

 fish five or six hours after it was dead, became luminous when 

 treated with ammonia water. 



The emission of light was also produced by electrical stimu- 

 lation. When the electrodes of an induction coil were applied 

 to the fish a brilliant glow of light was seen in every phosphores- 

 cent organ. These experiments were made on specimens taken 

 from under the rocks where they were guarding the young 

 brood. It is a curious fact that specimens taken by hook in 

 deeper water could not be made to show any phosphorescence 

 either by ammonia or by electric stimulation. It seems there- 

 fore that the power of emitting light is developed only in the 

 breeding season, but there is no evidence that the power is ever 

 exercised by the fish in its natural state. Evidently a special 

 investigation of this point is required. 



Among the most interesting and remarkable of all the 

 luminous organs of fishes are those which occur in two small 

 species of the East Indies, which were investigated by the 

 Dutch naturalists on the voyage of the Siboga. These fishes 

 are about 3 in. in length and appear to belong to the division 

 Perciformes of the Spiny-finned sub-order. One of them, Ano- 

 nialops grceffii, has been obtained at Amboina, Fiji, Paumotu 

 Archipelago, and the New Hebrides. Both of them are rather 

 common at the Banda Islands, where they were studied by 

 Professor Max Weber on the voyage of the Siboga. The 



