How small and unimportant is the difference between the changes which a caterpillar undergoes before becoming a moth, and those of a strobila before becoming a medusa. Yet in the one case we say the caterpillar does not die, but is changed (though, if the various changes in its existence be produced metagenetically, as is the case with many insects, it would appear to make a clean sweep of every organ of its existence, and start _de novo_, growing a head where its feet were, and so on—at least twice between its lives as caterpillar and butterfly); in this case, however, we say the caterpillar does not die, but is changed; being, nevertheless, one personality with the moth, into which it is developed. But in the case of the strobila we say that it is not changed, but dies, and is no part of the personality of the medusa. We say the egg becomes the caterpillar, not by the death of the egg and birth of the caterpillar, but by the ordinary process of nutrition and waste—waste and repair—waste and repair continually. In like manner we say the caterpillar becomes the chrysalis, and the chrysalis the moth, not through the death of either one or the other, but by the development of the same creature, and the ordinary processes of waste and repair. But the medusa after three or four cycles becomes the medusa again, not, we say, by these same processes of nutrition and waste, but by a series of generations, each one involving an actual birth and an actual death. Why this difference? Surely only because the changes in the offspring of the medusa are marked by the leaving a little more husk behind them, and that husk less shrivelled, than is left on the occasion of each change between the caterpillar and the butterfly. A little more residuum, which residuum, it may be, can move about; and though shrivelling from hour to hour, may yet leave a little more offspring before it is reduced to powder; or again, perhaps, because in the one case, though the actors are changed, they are changed behind the scenes, and come on in parts and dresses, more nearly resembling those of the original actors, than in the other.