I 
THE COLOURS OF ORGANISMS 
21 
We cannot here enter into a description of the 
phenomena of phosphorescence as they appear in all 
luminous organisms, but may conveniently add to 
the descriptions already given, an account of the 
process in terrestrial forms. For this purpose we 
may take Prof. C. Emery’s account of the phosphor¬ 
escence of Luciola italica , the Italian glow-insect. 
Here in the male the luminous organs are placed on 
the two last abdominal segments, each one appearing 
as a continuous surface although originally formed in 
two halves. In the female there are two luminous 
spots at the sides of the ventral surface of the fifth 
abdominal segment, the following two (the last) ab¬ 
dominal segments appear in dried specimens of the 
same pale colour as the fifth but are not luminous. 
The luminous organs consist each of a double layer, 
a ventral transparent one and a more dorsal chalk- 
white one containing masses of urates. Some of 
the large tracheal tubes run along the inner surface 
of the dorsal plate, and give off perpendicular 
branches which pass downwards and penetrate into 
the substance of the transparent layer, where they 
branch very freely, and come to lie close beneath 
the skin. 
A surface view of the luminous organ shows a 
series of round or oval spots corresponding to little 
masses of transparent cells surrounding the termina¬ 
tion of these tracheal branches; it is these spots 
which are luminous during life. They turn brown 
when treated with osmic acid, and are separated by 
broad darker intervals. More careful examination 
shows that these spots correspond to little cylinders 
formed by clusters of cells—the tracheal end-cells— 
