The Chemistry of Light-Production in Luminous Organisms. 175 



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 hght very intense. To a partially hght-adapted eye 

 the color is blue. In this respect the light differs markedly from the 

 yellowish white (to the dark-adapted eye) Ught of luminous bacteria 

 of Cavernularia or of the Japanese firefly, which is green to the par- 

 tially dark-adapted eye. Lund (s) 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 Ught to be decidedly bluish. There is no 

 inhibition of the light secretion in dayhght, as has been described for 

 other forms (4 and 5). 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. 



NATURE OF THE LIGHT-SECRETION. 



The gland-cells are almost completely filled with yellow material 

 which can be observed to be composed of yellow globules 2 to 6 micra 

 in diameter. These are extruded and dissolve to a colorless solution, 

 absolutely free of visible granules, which gives the light. The globules 

 are rather fluid in consistency, as the outline can sometimes be seen 

 to pass through amoeboid-like changes. 



If we examine the natural secretion of Cypridina in sea-water at 

 night, the hght appears perfectly homogeneous. No points of Hght 

 appear, such as might be due to granules, a condition wholly different 

 from that in the juice of Cavernularia, which contains visible granules, 

 and at night the light from these under the microscope gives the appear- 

 ance of a starry sky. 



If cypridinas be ground in a mortar and then examined at night, 

 numerous very bright points of hght appear, and these are greatly 

 increased by the addition of fresh water to the preparation. The 

 light undoubtedly comes from solution of the above-described yellow 

 globules and when they have dissolved no more points of light, but a 

 steady homogeneous glow, is to be observed. Electrical stimulation 

 by strong interrupted induced shocks does not intensify the light from 

 an extract of cypridinas, glowing faintly. 



PORCELAIN FILTRATION. 



Although no visible granules are found in the natural secretion of 

 Cypridina, an ultramicroscopic investigation was not undertaken on 

 account of lack of apparatus. 



