150 FABRE'S BOOK OF INSECTS 



timber ; inside, a mineral lid, a concave cover, all in one 

 piece, of a chalky white. Pretty often, but not always, there 

 is added to these two layers an inner casing of shavings. 



Behind this threefold door the larva makes its arrange- 

 ments for its transformation. The sides of the chamber are 

 scraped, thus providing a sort of down formed of ravelled 

 woody fibres, broken into tiny shreds. This velvety stuff is 

 fixed on the wall, in a thick coating, as fast as it is made. The 

 chamber is thus padded throughout with a fine swan's-down, 

 a delicate precaution taken by the rough grub out of kindness 

 for the tender creature it will become when it has cast its skin. 



Let us now go back to the most curious part of the furnish- 

 ing, the cover or inner door of the entrance. It is like an oval 

 skull-cap, white and hard as chalk, smooth within and rough 

 without, with some resemblance to an acorn-cup. The rough 

 knots show that the material is supplied in small, pasty 

 mouthfuls, which become solid outside in little lumps. The 

 animal does not remove them, because it is unable to get at 

 them ; but the inside surface is polished, being within the 

 grub's reach. This singular lid is as hard and brittle as a 

 flake of limestone. It is, as a matter of fact, composed solely 

 of carbonate of lime, and a sort of cement which gives con- 

 sistency to the chalky paste. 



I am convinced that this stony deposit comes from a par- 

 ticular part of the grub's stomach, called the chylific ventricle. 

 The chalk is kept separate from the food, and is held in reserve 

 until the right time comes to discharge it. This freestone 

 factory causes me no astonishment. It serves for various 

 chemical works in different grubs when undergoing trans- 

 formation. Certain Oil-beetles keep refuse in it, and several 

 kinds of Wasps use it to manufacture the shellac with which 

 they varnish the silk of their cocoons. 



When the exit way is prepared, and the cell upholstered 

 in velvet and closed with a threefold barricade, the industrious 

 grub has finished its task. It lays aside its tools, sheds its 

 skin, and becomes a pupa weakness personified, in the 

 swaddling-clothes of a cocoon. The head is always turned 



