STUDIES ON BIOLUMINESCENCE. 283 



of light. The phenomenon is unquestionably one of cytolysis, 

 by diminution of osmotic pressure, by heat, or by addition of 

 specific substances. In the extract- there are probably intact 

 photogenic cells which dissolve with production of light. In 

 addition I believe the solution of photogenic granules is also 

 accompanied with the emission of light, because one can very 

 easily see, under the microscope at night, the sudden appearance 

 of a disc of light, too small to be the illumination of a cell, but 

 capable of interpretation as the light from a single granule 

 within the cell. 



Extracts of dEquorea which should contain lucif erase give m> 

 light with extracts of JEqiiorea which should contain luciferin. 

 The same is true for Mitrocoma and for crosses of luciferin and 

 luciferase of Cypridina with these two medusae. Every attempt 

 to demonstrate these substances has given negative results. 

 The reasons for this are discussed in another paper, to appear 

 shortly. 



It is reported that many luminous forms produce no light in 

 the daytime, the power only appearing with the approach of 

 dusk or if the animals are kept in the dark for some time. This 

 is true of some forms but not of these medusae. The four kinds 

 of luminous medusae, sEquorea, Mitrocoma, Phialidium and 

 Stomatoca, were collected in bright sunlight and brought by an 

 assistant to the dark room where I had been adapting my eyes, 

 to the dark for one half hour. All four forms luminesced im- 

 mediately on stimulation and just as brightly as at night. The> 

 ctenophore, Bolina, did not luminesce even after ten minutes,, 

 when brought into the dark from strong sunlight, but did lu- 

 minesce after thirty minutes. There is no doubt that Bolina, 

 a further discussion of which follows, is affected by sunlight but 

 these four medusae are certainly not. Noctiluca appears to have 

 its luminescence inhibited by strong sunlight also. 



EXPERIMENTS ON CTENOPHORES. 



At Friday Harbor, three species of ctenophores occur, Bolina 

 sp. ?, Pleiirobrachia sp. ?, and Beroe sp. ?, but only the first was 

 common during my stay. Bolina luminesces readily at night. 

 Pleurobrachia did not luminesce even on crushing and Beroe 

 only gives a diffuse flash of light on vigorous agitation. 



