THE CATERPILLAR KIND. 171 



parts of the animal which is contained within it ; but a-» to the 

 various colours which it is seen to assume, they are rather the 

 effect of accident ; for the same species of insect does not at all 

 times assume the same hue when it becomes an aurelia. In some, 

 the beautiful gold colour is at one time found ; in others it is 

 wanting. This brilliant hue, which does not fall short of the best 

 gilding, is formed in the same manner in which we see leather 

 obtain a gold colour, though none of that metal ever enters into 

 the tincture. It is only formed by a beautiful brown varnish, 

 laid upon a white ground ; and the white thus gleaming through 

 the transparency of the brown, gives a charming golden yellow. 

 These two colours are found, one over the other, in the aurelia 

 of the little animal we are describing ; and the whole appears 

 gilded, without any real gilding. 



The aurelia thus formed, and left to time to expand into a 

 butterfly, in some measure resembles an animal in an egg, that 

 is to wait for external warmth to hatch it into life and vigour. As 

 the quantity of moisture that is inclosed within the covering of 

 the aurelia, continues to keep its body in the most tender state, 

 so it is requisite that this humidity should be dried away, before 

 the little butterfly can burst its prison. Many have been the 

 experiments to prove that nature may in this respect be assisted 

 by art ; and that the life of the insect may be retarded or quick- 

 ened, without doing it the smallest injury. For this purpose, it 

 is only requisite to continue the insect in its aurelia state, by 

 preventing the evaporation of its humidity, which will conse- 

 quently add some days, nay weeks, to its life ; on the other hand, 

 by evaporating its moisture in a warm situation, the animal as- 

 sumes its winged state before its usual time, and goes through 

 the offices assigned its existence. To prove this, IVI. Reaumur 

 inclosed the aurelia in a glass tube, and found the evaporated 

 water which exhaled from the body of the insect, collected in 

 drops at the bottom of the tube ; he covered the aurelia with 

 varnish, and this making the evaporation more difficult and slow, 

 the butterfly was two months longer than its natural term in com- 

 ing out of its case ; he found, on the other hand, that by laying 

 the animal in a warm room, he hastened the disclosure of the 

 butterfly ; and by keeping it in an ice-house in the same manner, 

 he delayed it. Warmth acted, in this case, in a double capacity, 

 invigorating the animal, and evaporating the moisture. 



The aurelia, though it bears a different external appearance, 

 nevertheless contains within it all the parts of the butteifly in 

 perfect formation, and lying each in a very orderly manner, 

 though in the smallest compass. These, however, are so fast 

 and tender, that it is impossible to visit without discomposing 

 them When either by warmth, or increasing vigour, the parts 



