Y. HANEDA 351 



flash at 25° C is two to three seconds. The flashing is spontaneous; 

 no kiminescence appears on stimulation. The intensity of each flash 

 is the same and fairly bright, visible in electric light if shaded by the 

 hand. 



The luminescence comes from luminous cells, not from luminous 

 bacteria. The luminous organs, consisting of large luminous gland 

 cells, lie below the mucous gland of the foot and surround its open- 

 ing, but no luminous material is secreted to the outside. Hence this 

 snail is self-luminous, and the light is intracellular. 



In sections, the luminous tissue can be easily distinguished. The 

 luminous organ of a shell 15 mm in diameter is 2 mm long and 1.5 

 mm wide. The luminous cells are pale green, while the mucous cells 

 of this region are yellowish orange when stained by safranin. 



Luminous Marine Snails 



Lu::.inous species of Gastropoda Prosobranchiata are also very 

 rare. According to Turner (see Harvey, 1952) Tonna galea Linne, a 

 marine Gastropoda, is luminescent. When this animal is moving about 

 with its foot well extended, it emits a greenish white light. 



We have found two species of luminous Gastropoda on the beach 

 of Borawazawa, Sueyoshi Village, Hachijo Island. During ebb tide on 

 Apiil 23, 1953, my friend, Mr. H. Okuyama, saw some small marine 

 snails emit light as they rolled in the sea water when he raised a 

 stone. We were very much astonished and collected many specimens, 

 examining them repeatedly to find out if these marine snails were 

 really luminous, or were luminous only because of eating some lumi^ 

 nous matter, or were infected luminous bacteria. As a result of these 

 observations, I decided the snails are truly luminous, possessing a 

 luminous organ on their mantles. 



These luminous marine snails, shown in Fig. 4, are very small. The 

 shell, a beautiful pale pink with brown bands, is 10.5 mm high and 

 has a diameter of 6 mm. The scientific name of this snail is Planaxis 

 viratus Smith, identified by Dr. I. Taki of the National Science Mu- 

 seum in Tokyo. I found another species, Planaxis perescelida Dall, in 

 our collection and this also had the same luminous organ and emitted 

 light. This species is rather more slender than the Planaxis viratus. 

 Its height is 12 mm and its diameter 5 mm. The color is dark brown 



