An inverse experiment was essential. A Dung-beetle thrives on rotten leaves; shall I be equally successful in rearing an eater of vegetable refuse on dung? From the heap of dead leaves accumulated in a corner of the garden for mould, I obtain a dozen half-grown larvæ of the Golden Cetonia. I install them in a glass jar, with no other food than Mule-droppings which have acquired the proper consistency by a few days’ exposure to the air on the high-road. The stercoral ration is welcomed by the future rose-dweller. I cannot see any signs of hesitation or repugnance. When half-dry, the Mule’s fibrous scraps are consumed as readily as the leaves brown with decay. A second jar contains larvæ fed in the normal fashion. There is no difference between the two groups in the matter of appetite and healthy looks. In both cases the metamorphosis is properly accomplished. This double success gives food for thought. Certainly the Cetonia-grub would have nothing to gain if it thought fit to abandon its heap of dead leaves in order to exploit the Mule-droppings in the road; it would be leaving inexhaustible abundance, pleasant moisture and perfect security in exchange for a scanty, perilous diet, trampled underfoot by the passers-by. It will not commit this act of folly, however alluring the bait of a new dish. It is not the same thing with the larva of the Geotrupes. In the open fields, the droppings of beasts of burden, without being scarce, are not by any means to be met with everywhere. They are found chiefly on the roads, which, encrusted with macadam, offer an insuperable obstacle to burrowing. On the other hand, half-rotten dead leaves accumulate everywhere in inexhaustible quantities. What is more, they abound on loose soil, which is easily excavated. If they are too dry, there is nothing to prevent their being carried down to such a depth that the moisture of the soil will give them the requisite pliability. An insect is not a Geotrupes, an earth-borer, for nothing. A silo sunk a few inches deeper than the ordinary burrows would make an excellent steeping-vat. Since the Geotrupes-grubs thrive on a column of rotten leaves, as my experiments have proved, it would seem that the maker of dung-sausages would gain greatly by slightly modifying her trade and substituting fermented leaves for stercoral matter. The race would be the better for the change and would become more numerous, since there would be plenty of food in perfectly safe places. If the Geotrupes does nothing of the kind, if it has never even attempted to do so, apart from my artificial methods of rearing, it is because the regimen is not determined merely by the appetites of the consumers. Economic laws regulate the diet and each species has its portion, in order that nothing shall be left unused in the treasury of unorganizable matter.