352 Proceedings of Royal Society of Edinburgh. [july 4 , 
tail : that these could all be seen, easily by the unaided eye : that 
the pair close to the eyes was first and most brilliantly illuminated, 
and then the light, which was bluish white, spread to the other 
organs in the trunk and tail : that after a brilliant flash had been 
emitted, the organs glowed for some time with a dull light : that 
the light was given out at will by the animal, and usually but not 
always on irritation : that subsequent flashes became less and less 
bright till the animal appeared to lose the power of emitting light : 
that if the organs were removed by the forceps, the points of the 
latter glowed brightly for some time, and when the animal was 
dying the whole body was frequently illuminated by a diffused light: 
that the phosphorescent organs appeared under the microscope as 
pale red spots with a central clear lenticular body, and the light 
came from the red pigment. It is further mentioned that in August 
1880 Mr John Murray observed at night, on the surface of the sea 
in the Faeroe Channel, large patches and long streaks of apparently 
milky- white water, and the tow-nets caught in these places immense 
numbers of Nyctiphanes norvegica , M. Sars, about half the size of 
the adult, and the peculiar appearance of the water seemed to be due 
to the diffused light emitted from the phosphorescent organs of this 
species. 
That the organs, erroneously called accessory eyes, were in reality 
luminous or “ phosphorescent ” organs was definitely asserted by Prof. 
G. C. Sars, in his Keport on the Schizopoda of the “Challenger.” He 
gives an account of their structure, but does not discuss very fully the 
questions concerning the method and mechanism of the production of 
light. Mr W. Patten* only last year has again attempted to maintain 
that these organs are eyes and not luminous organs ; but in view of 
the evidence of Sars and others and of our own experiments, Mr 
Patten’s arguments need no special refutation; they are indeed con- 
tradicted sufficiently by the postscript which is added to his paper 
by Drs Giesbreclit and Paul Meyer, who personally observed the 
luminosity of Euphausia. 
We have studied these organs and their function in Nyctiphanes 
norvegica, Sars, which is abundant in certain deep places in the 
Clyde sea-area. We obtained it in 95 fathoms off Brodick Bay, by 
* “Eyes of Molluscs and Arthropods,” Mitt, aus der Zool. Stat. zn Neapcl , 
1886. 
