20 NATURAL HISTORY. [cH. I. 



a rational explanation of this strange statement, 

 " that wher6 the back of the caterpillar is placed, 



there the belly and legs of the animal into which it 

 is changed are situated ; and on the contrary, where 

 the belly and legs were, there the back of the ani- 

 mal, which by transformation was produced from 

 the caterpillar, is discovered. And," adds he, " this 

 wonderful transformation is effected in a short 

 space of time, so as to be distinctly observed, be- 

 cause as soon as the skin is shed this transforma-' 

 tion manifestly appears." Shortly after entering 

 the pupa state the chrysalides of various kinds of 

 butterflies assume, in a greater or less degree, a bur- 

 nished golden appearance, whence they obtained the 

 names of chrysalis and aurelia, which were subse- 

 quently applied to the whole of the lepidopterous 

 pupae. The alchymists, indeed, mistook this for real 

 gold ; and, as Messrs. Kirby and Spence observe, 

 " referred to the case as an argument in favour of 

 the transmutation of metals." But Reaumur found 

 that this appearance is owing to the shining white 

 membrane immediately below the outer skin, which, 

 being of a transparent yellow, gives a golden tinge 

 to the former, in the same way that tinfoil, when 

 covered with a yellow varnish, assumes the metal- 

 lic appearance which we see in gilt leather. He 

 mentions too, " that for the production of this ef- 

 fect it is essential that the inner membrane be moist ; 

 whence may be explained the disappearance of the 

 gilding as soon as the butterfly is ready to escape 



