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General Characteristics of Light-Production

light, sea-water, squid and surface

GENERAL CHARACTERISTICS OF LIGHT-PRODUCTION.

The structure of the luminous organs and the habits of this form have been well described by Ishikawa (31) and Sasaki (32). The organs are found on the tip of the ventral arms (3 in number), on the eyeball (5 in number), and over the ventral surface of the body (many). Only those of the arm-tips are brilliant enough to make chemical studies feasible. Their light is a brilliant bluish white like that of Cypridina. The intensity is high, but is no doubt due in large part to the reflectors present in the gland. The luminous material is burned within the cells. The animal is a deep-sea form, coming to the surface near shore to breed in certain bays of the Japanese coast, notably Toyama Bay. The surface-water of this bay is brackish and the animals will not live in it for even one hour. The deeper waters of the bay are more salty and in these the squid will live for a longer time if the water is changed to remove the poisonous ink. If oxygen be forced through fine pores into the water, the squid, as Professor Shoji, of Kyoto 'University, has shown, will live perhaps 8 hours, but this is the maximum. It will be seen, therefore, that the animal is extremely delicate and it is not sur prising to find it of little value for chemical research. The arm-tip light-organs respond only to stimulation and the response disappears in 5 to 10 minutes after the animals are removed from sea-water. If

the arms are cut off and placed in sea-water the light-producing sub stance entirely disappears in 30 to 60 minutes, as we can determine by grinding in a mortar. No light appears. The arm-tip light-organs become exhausted very rapidly if continually stimulated, and the light disappears very quickly after the organs have been ground in a mortar with water or sea-water.

The light of the skin-organs scattered over the ventral surface lasts much longer, and even after removal from the sea-water for 1 hour they will give a light which is more yellowish if stimulated electrically. The response is localized in the region about the electrodes.

The eye-organs are difficult to stimulate. Their light is weak and similar to that of the skin-organs.

The squid are caught at night in enormous numbers during April, May, and June by the fishermen, and Professor C. Ishikawa informs me that if brought into a dark room in the daytime they give light. The squid for this experiment were caught at 3 a. m. and tested about 8 a. m.—i. e., 3 or 4 hours after daylight had appeared. There is no inhibiting influence of daylight on light-production, as described by Peters (4) for Ctenophores or Moore (5) for various luminous plankton forms. Neither have I observed any such influence of light with Monocentris, Cypridina, Cavernularia, Pennatula, or Noctiluca.