356 Proceedings of Royal Society of Edinburgh. [july 4 , 
of the argentea. One of us was tempted to conclude from these 
facts that the luminosity of the organs in the living animal was entirely 
and exclusively due to the purely physical property of fluorescence 
in the internal portion of the argentea. But this conclusion is quite 
inconsistent with the intermittent emission of the light and its 
dependence on stimulation. Moreover, in other luminous organs, 
e.g., Lamypris splendidula , the light has been shown to come from 
a thick mass of cells, and no layer resembling the argentea of 
Nydiphanes is present. At present we conclude that probably the 
posterior cell layer in Nydiphanes is the active agent in producing 
light when acted on by a nervous impulse, and that the light is 
much intensified by the fluorescent property of the surface of the 
argentea. Of the function of the central mass of rod or fibres we 
have ascertained nothing at all. The lens is obviously there in 
order to concentrate the light, while the anterior cellular cap is 
merely a transparent cornea. The fibrous iris-like ring round the 
lens perhaps acts as a diaphragm, though it undoubtedly is not 
pigmented and is transparent. We hope shortly to make renewed 
attempts to elucidate the mechanism of the organs. 
6. On a Constant Daniell Cell, for nse as a Standard of 
Electromotive Force. By Cosmo I. Burton, B.Sc., F.C.S. 
This cell consists of two tubes about three inches long and half 
an inch in diameter, sealed at one end, and connected together near 
the closed end by a glass tube about four inches long, having a 
glass tap in the middle. 
The hole through the plug of the tap is filled with plaster of 
Paris, made as nearly as possible flush with the glass surfaces. This 
plaster plug serves as a porous septum between the two tubes, which 
represent respectively the two compartments of a Daniell cell — the 
one tube containing a copper rod immersed in a saturated solution 
of copper sulphate, the other a zinc rod in a solution of zinc sul- 
phate, of as nearly as may be the same density as the copper 
solution. The cell is designed for use only with the quadrant 
electrometer, and must never be short-circuited. 
When the cell is used the tap is turned “on,” i.e ., so that the 
