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General Character of Light and of Luminous Glands

secretion, cypridina and readily


Cypridina hilgendorfii is a strongly negatively heliotropic ostracod best obtained at night by lowering into the water fish heads, on which the animals feed. It may be caught the year round, but is most abundant during August and September in Sagami Bay, Japan. Another non-luminous species (Cypridina x.) is often obtained from the fish heads together with C. hilgendorfii. It is positively heliotropic to lamplight. C. hilgendorfii is so strongly negatively heliotropic that it is not readily caught on moonlight nights and avoids a shore with many electric lights.

The light-giving material of Cypridina is a secretion formed in a special gland of yellow spindle-shaped cells, opening near the mouth.' In adult living cypridinas the gland-cells form a cylinder about 0.64 mm. by 0.24 mm., having a volume of about 0.0003 c.c. The secretion is readily formed upon agitation of the animal and is easily visible in a room in the daytime. To the dark-adapted eye the color is decidedly bluish and the light very intense. To a partially light-adapted eye the color is blue. In this respect the light differs markedly from the

yellowish white (to the dark-adapted eye) light of luminous bacteria of Cavernularia or of the Japanese firefly, which is green to the par tially dark-adapted eye. Lund (3) describes a Cypridina squamosa (?) and a Cyclopina gracilis from Montego Bay, Jamaica, which gave an "intensely luminous greenish yellow secretion." Most observa tions, however, record the light to be decidedly bluish. There is no inhibition of the light secretion in daylight, as has been described for other forms (4 and 3). When first caught, cypridinas give off the secretion readily, sometimes upon mere contact with the surface film of water, but if they are kept in the laboratory the secretion is not given off so readily. Removal from sea-water also inhibits the ejec tion of the secretion and it is necessary to squeeze the animal rather strongly before the secretion is given out. Electrical stimulation also calls forth the production of an abundant light-secretion.