282 Natural history. [ch. xvi. 



supply of nourishment originally provided for them 

 begins to fail. 



When about to undergo their metamorphosis, some 

 of these insects quit their habitations, while others 

 continue in them. The latter class adopt a precau- 

 tion which well deserves attention; the range of the 

 gallery which they have mined is not equidistant 

 from the upper and lower membranes of the leaf, 

 being much nearer the former ; hence, the caterpillar 

 cannot be seen through the under surface of the leaf, 

 because a considerable portion of the parenchyma, 

 or pulpy matter, remains unconsumed between the 

 floor of the gallery and the inferior membrane of 

 the leaf. On the upper surface, however, the cater- 

 pillar eats away all the parenchyma ; so that on that 

 side the epidermis alone forms a thin and vaulted 

 roof, through which the insect may be readily seen. 

 But when about to assume the defenceless state of 

 a chrysalis, its instinct impels it to seek a place of 

 greater security: with this view it dives from its 

 gallery, making its may directly downwards until it 

 reaches the lower surface of the leaf, where it dis- 

 tends a portion of the parenchyma, which was left 

 uneaten and interposed between the lower epidermis 

 and the gallery of the insect : at this period it would, 

 therefore, be vain to look for the insect in its usual 

 gallery, near the upper skin of the leaf, and it might 

 be concluded that the little inhabitant had entirely 

 forsaken its original abode ; but on turning up the 

 leaf, a small and rounded protuberance may be per- 

 ceived, under which the creature has been instinct- 

 ively taught to shelter itself, during its torpid state, 

 from its natural enemies. 



Many of these mining caterpillars turn into moths, 

 which, had they been as large as they are beautiful, 

 would have presented an appearance marvellously 

 brilliant. Assisted by a magnifier, the eye may per- 

 ceive the little creature radiant with shining gold, 

 its winss streaked here and there with silver of daz- 



