It is very easy to put the fact of the breathing of the pupa, inanimate as it appears, to a certain test. By taking a wine-glass half full of water, and putting it under an air-pump, and then exhausting the air, we shall be able to extract the air which exists dissolved in the water: or some water that has been boiled and allowed to cool will do as well. If we now put a pupa into this water, and again exhaust the air from the receiver, we shall notice, at the second stroke of the piston, a number of little jets of air come from the insect's body at the places where the spiracles are situated, thus clearly proving that the creature breathes air by this apparatus. The fact may be tested also in another way--and both this and the preceding experiment are due to the ingenious Réaumur. He took the pupa of a butterfly, and suspending it by a thread immersed it half way down in oil; on taking it out after some time it was still alive and apparently uninjured, the reason being, that the entire number of its breathing-holes were not covered. He took another of the same species, and plunged it entirely under the oil, and taking it out after a time it was found to be quite dead; in fact it had been suffocated by the air being shut out from its breathing apparatus, and that as effectually as if it had been one of ourselves lying at the bottom of the sea. We may say, therefore, with perfect accuracy, that though the pupa, this seemingly un-living object, neither moves nor eats, nor in any other way gives us a sign that it is alive, except in a few cases, and that in its advanced stages, we can, nevertheless, prove it to be living; as it can be shown that it has the power of breathing; and if it breathes, it lives.
We may take the liberty of appropriately appending to this statement a most interesting and delightfully-told anecdote, from the pages of the Baron de Geer, of an insect whose larva lives in the water, but whose pupa is an air-breathing creature, and consequently would perish if the change from larva to pupa were to take place under water, without some especial contrivance to furnish it in the pupa form with a supply of air. Yet how can this be, when the insect is under water the whole time up to its becoming a perfect moth? We shall hear:--