168 INSECT TRANSFORMATIONS. 



leaves, beinj^ thence protected, remain soft and 

 pulpy. But as soon as the inner leaves receive au 

 accession of sap, which rises from the roots on 

 the return of sprino;, their vessels swell and their 

 nervures expand ; while the outer leaf, from its ves- 

 sels being shrunk and partly obliterated, undergoes 

 little change besides being pushed out and some- 

 times entirely thrown off by the growth of the inner 

 leaves, which it had previously inclosed. It may he 

 remarked, also, that this outer envelope of a bud is 

 not united with the inner leaves by any interlacing of 

 their substance or of their vessels, though in some 

 cases there is an adhesive gluten which partly binds 

 them together ; but this is never so strong as to 

 prevent the expansion of the leaves. On comparing 

 one of the bud-envelopes thus thrown off, we can 

 scarcely persuade ourselves that so small a covering- 

 could ever have contained the large spreading leaves 

 which have burst from them. 



A caterpillar corresponds in several circumstances 

 with the leaf-bud. The outer skin encloses a suc- 

 cession of several other skins, each becoming more 

 delicate, soft, and indistinct than the one exterior to 

 it, but gradually, like the expanding leaves, growing 

 more • substantial and firm as it receives a supply 

 of nutriment. The chief mechanical difference be- 

 tween the leaves folded up in the bud and the suc- 

 cessive caterpillars enveloped within the skin of one 

 newly hatched, is that the leaves in the bud receive 

 all their nourishment through their foot-stalks from 

 the root of the tree, whereas the caterpillar is nou- 

 rished from within by the food digested in its stomach. 

 The superfluous nourishment, usually in considerable 

 quantity, and called the fat of the caterpillar, appears 

 to lie between the successive skins, in a similar way 

 to the adhesive gluten in the leaf-bud. But as the 

 first inner skin expands and increases in consistence, 



