I see other nervures in the intervals, pale and very fine.

Finally, still more delicate, and running transversely, a number of very short nervures complete the pattern.
Certainly this resembles a rough sketch of the future wing-case; but how different from the mature structure! The disposition of the radiating nervures, the skeleton of the structure, is not at all the same; the network formed by the cross-nervures gives no idea whatever of the complex final arrangement.

The rudimentary is succeeded by the infinitely complex; the clumsy by the infinitely perfect, and the same is true of the sheath of the wing and the final condition of its contents, the perfect wing.
It is perfectly evident, when we have the preparatory as well as the final condition of the wing before our eyes, that the wing-sheath of the larva is not a simple mould which elaborates the tissue enclosed in its own image and fashions the wing after the complexities of its own cavity.
The future wing is not contained in the sheath as a bundle, which will astonish us, when expanded, by the extent and extreme complication of its surface.

Or, to speak more exactly, it is there, but in a potential state.

Before becoming an actual thing it is a virtual thing which is not yet, but is capable of becoming.