352 LUMINOUS ORGANISMS OF FAR EAST 



with pale black or dark brown bands. Each species is widely dis- 

 tributed in southern Japan. 



When the animal is under natural conditions on a rock with its 

 foot well extended, no Hght can be seen. However, the light appears 

 on strong stimulation. If many specimens are placed in a bottle and 



^«t^ 



Fig. 4. The luminous marine snail, Planaxis viratus, from Hachijo Island, Japan. 



well shaken in the dark, some of them become luminous and twinkle. 

 The light continues one or two minutes and then gradually disap- 

 pears. If the body of the snail is irritated, the Ught reappears, and 

 if placed in fresh water, the light continues for a longer time. 



When the animal is taken out of the shell by crushing the shell and 

 is observed under a binocular or low power microscope in the dark, 

 the luminous region is found to be on the dorsal part of the mantle 

 in a limited area, as shown in Fig. 5. Under the microscope number- 

 less luminous dots can be seen appearing or disappearing. The lumi- 

 nescence of this animal is intracellular and the luminous organ con- 



