INTRODUCTION. 
83 
agreeable hues. Those of the Swallow-tail and 
Purple Emperor are of a fine green, resembling their 
respective caterpillars : the ground colour of that of 
the common Cabbage Butterfly is greenish-yellow, 
marked with small black points, somewhat arranged 
in lines ; while that of the Black-veined White 
(Plate III. fig. 4.) is yellow, streaked and spotted 
with black. But many chrysalides are decorated in 
a more sumptuous manner, some of them appearing 
entirely covered, and others spotted with golden- 
yellow of the highest metallic lustre. It is this co- 
lour which caused the Greek name Chrysalis, and 
the Latin one Aurelia, to be applied to the kinds so 
distinguished, although these terms are now used 
indiscriminately in relation to the whole. Among 
British chrysalides, the kinds that exhibit most of 
this metallic brilliancy, are those that produce flies 
belonging to the genera Argynnis and Vanessa. That 
it is not a superficial application, is proved by its 
disappearing as soon as the enclosed fly escapes. 
The observations of Reaumur have shewn that it is 
owing fo the transparency of the outer skin, which 
is of a yellow colour, and gives a golden tinge to 
a shining white membrane lying immediately be- 
neath it. A similar effect is sometimes produced by 
artificial means. 
The duration of the pupa state varies greatly in 
different species, and even in the same species, ac- 
cording to circumstances. Thus, the chrysalis of 
the Swallow-tail Butterfly ( P. Machaon J, when the 
