This is one of the most important subjects in the whole round of natural history.

The metamorphoses of insects, with which every one is familiar, are generally effected abruptly by a few stages; but the transformations are in reality numerous and gradual, though concealed.

A certain ephemerous insect (Chloeon) during its development, moults, as shown by Sir J.

Lubbock, above twenty times, and each time undergoes a certain amount of change; and in this case we see the act of metamorphosis performed in a primary and gradual manner.

Many insects, and especially certain crustaceans, show us what wonderful changes of structure can be effected during development.