STUDIES ON BIOLUMINESCENCE. 285 



stimulated after exposure to sunlight or do they fail to manu- 

 facture photogenic substances as a result of exposure to sunlight? 

 One alternative supposes the cell to contain photogenic material 

 which for some reason cannot he oxidized; the other, that no 

 photogenic material is formed in the sunlight and the disap- 

 pearance of that which has been formed. Some evidence can 

 be obtained for the latter view by breaking up the cells of cteno- 

 phores which have been previously exposed to daylight. If no 

 luminescence is produced the effect of light must be to prevent 

 the manufacture of photogenic material. If luminescence occurs 

 on breaking up of the photogenic cells previously exposed to day- 

 light, the inhibitive actions of light must be on the stimulation 

 mechanism. 



If Bolinas, which have been previously exposed to daylight, are 

 crushed through four layers of cheescloth, no light whatever 

 appears during the crushing or on adding fresh water to cytolyse 

 the photogenic cells. Similar Bolinas, kept in the dark for one 

 half hour, give a bright luminescence under the same treatment. 

 If this extract of crushed Bolinas, which had been previously 

 exposed to sunlight, is allowed to stand in the dark for one half 

 hour and then fresh water added, no light will appear. Whole 

 Bolinas after sun illumination will again luminesce if kept in 

 the dark for one half hour. This shows that there is no pre- 

 formed photogenic material in sunlight exposed Bolinas and that 

 none can be formed in crushed material even in the dark. The 

 sunlight must therefore act to prevent the formation of photo- 

 genic substance rather than to prevent its oxidation on stimu- 

 lation. Why sunlight causes the disappearance of photogenic 

 material already formed is a question awaiting solution. 



EXPERIMENTS ON A SEA PEN, Ptylosarcit*. 



Ptylosarcus is dredged at Friday Harbor in fairly deep water. 

 Some of the specimens may be two feet long. The colony consists 

 of a stalk without fronds buried in the sand and a stem with 

 fronds that bear polyps only along the outer edge. The polyps, 

 but not the surface of the fronds, are luminous. The stalk is 

 not luminous but the stem has two luminous areas running the 

 length of it and one non-luminous area between these. 



