12 SURVEY OF LUMINOUS ORGANISMS 



sessing a single nucleus and a sap vacuole into which substances may 

 be injected or sap withdrawn. It also possesses a flagellum and a ten- 

 tacle, whose movement can be studied. In addition there are visible 

 protoplasmic changes on electrical stimulation. 



There are also interesting osmotic relations in Noctiluca, connected 

 with a specific gravity less than that of sea water. The low density 

 is due to a definite salt content, not to oil droplets. Permeability, 

 movement, and light emission can all be studied together in this 

 single cell — a most unusual situation. The relation between oxygen 

 pressure, temperature, hydrostatic pressure, pH, salts, drugs, etc., and 

 light emission and movement should be worked out in detail. 



The smaller dinoflagellates are not as favorable material as Nocti- 

 luca for the cell physiologist. However, the relation between oxygen 

 pressure and light emission should be studied carefully. The Radio- 

 laria do not require oxygen for luminescence, and this peculiarity 

 may be more widespread among Protozoa than is now realized. Day- 

 night rhythms of luminescence might be carefully tested in all species. 

 Should it prove feasible to culture luminous Protozoa in large numbers 

 under laboratory conditions, they should be as valuable for biochemi- 

 cal work as the luminous bacteria. 



The great groups of luminous coelenterates and ctenophores behave 

 alike in many ways. The luminous tissue can be ground in sea water 

 to a dark extract that will give a brilliant light when added to fresh 

 water. Luminescence comes from granules which dissolve with light 

 emission as a result of treatment with many agents, such as saponin, 

 which cause the cytolysis of cells. The chemistry of these forms is 

 completely unknown and offers a virgin field for investigation, since 

 material can no doubt be prepared by modern methods of freeze- 

 drying. As we have seen, in some species dissolved oxygen is not 

 necessary for luminescence and in other species photochemical changes 

 in the luminescent system prevent luminescence after the animal is 

 exposed to daylight. 



In addition, the physiology of luminescence in medusae, pennatulids, 

 and ctenophores presents many problems connected with excitation of 

 light by luminor nerves and reflex transmission of impulses. A begin- 

 ning has been made by the work of Parker (1920), Buck (1953), and 

 Harvey and Chang (1954), but much more needs to be done. The 



