VII 
THE COLOURS OF THE LEPIDOPTERA 
157 
cell, but as development proceeds the protoplasm 
is withdrawn, leaving the scale empty ; the forma¬ 
tive cell also undergoes a process of degeneration. 
The scale itself, of course, consists of chitin formed 
apparently at the expense of the original protoplasm. 
Mr. Mayer’s account of the formation of the 
pigments is as follows:—After the protoplasm is 
withdrawn from the scale, this for a time is entirely 
empty and contains nothing but air; a little later 
the haemolymph of the pupa enters it and gives it 
an ochre-yellow colour. The fresh haemolymph is 
of an amber colour, but when shed it speedily turns 
a turbid ochre-yellow colour, the same colour as that 
manifested by the lymph of the scales. After re¬ 
maining for about twenty-four hours in the ochre- 
yellow stage, the scale begins to acquire gradually 
the characteristic colours. Mayer is of opinion that 
this development proves that the pigments are formed 
from the degenerating haemolymph contained in the 
scale. He endeavours to prove his position by 
recounting some observations on the reactions of the 
haemolymph to chemical agents. Thus “ warm con¬ 
centrated nitric acid ” gives a “ chrome-yellow ” colour 
changing to “ reddish-orange ” with ammonia, the 
colour being very like that of a pigment-band on the 
wing of the moth experimented with (Samia cecropia). 
In what respect, however, the colour differs from that 
always given by proteids when treated with these 
reagents—which of course constitute the xantho¬ 
proteic reaction—is not mentioned. Although the 
reagents employed by Mr. Mayer were all too 
powerful for us to lay any stress on the chemical 
side of his work, yet on the histological side there 
