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 Argyiinis 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 to 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. MachaonJ, when the 



