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 is withdrawn, leaving the scale empty ; the forma- 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 withdrawn from the scale, this for a time is entirely 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 



