1887 .] Mr J. T. Cunningham on Nyctiphanes norvegica. 355 
from which particular portion of the organ the light proceeded. 
The results of this examination were afterwards verified by both of 
us together. In this investigation, no evidence was obtained in 
support of Sars’ opinion that the light principally emanated from 
the central mass of fibres behind the lens. When the organ was 
crushed beneath a cover glass, and examined in daylight, it was not 
difficult to separate the different layers from one another. The 
exterior pigment cells were in this process dispersed, and every 
other part of the organ, with a single exception, was found to be 
perfectly colourless and transparent. The exception was the inner 
superficial portion of the stratified layer, which may for the time be 
named the argentea. This portion, when viewed by transmitted light, 
was seen to have a beautiful luminous purple colour, like a sunset 
tint. The purple was reddish at first, but gradually became more 
blue as time went on, till after about half an hour the colour was a 
deep blue or violet. When the transmitted light was shut off, and 
the preparation was viewed by reflected light without a condenser, 
the colour of the same region was the complementary tint of that seen 
by transmitted light. The peculiarity of this colour was, that it 
appeared to be luminous ; that is, no part of the preparation could 
be seen at all in the field but this colour, which shone with a greenish- 
yellow light. When the light was entirely excluded, the whole 
preparation was invisible. It follows from this, that the inner 
surface of the argentea possesses in a marked degree the property of 
fluorescence. It was afterwards found that such a preparation, when 
viewed in the dark with the naked eye, contained a luminous spot, 
and this spot was always found to be the inner portion of the 
argentea. The phosphorescence was not visible through the micro- 
scope, simply because the light was absorbed by the lenses ; but 
when light fell on the preparation, although it was not sufficient to 
render visible other parts of the organs, the inner surface of the 
argentea, by its fluorescent action on the most refrangible rays of the 
spectrum, became visible, just as in the case of uranium glass. 
Another fact is of great interest. When a living specimen of 
the animal is crushed between the hands and rubbed with the 
fingers, certain pieces of the mangled tissue are seen to be luminous 
in the dark. Such pieces can be picked off with the forceps and 
examined with the microscope, and are always found to be morsels 
