Madam How invented that ages and ages before she thought of cockles, and the animal which lived inside that shell was as different from a cockle-animal as a sparrow is from a dog.

That is a Terebratula, a gentleman of a very ancient and worn-out family.

He and his kin swarmed in the old seas, even as far back as the time when the rocks of the Welsh mountains were soft mud; as you will know when you read that great book of Sir Roderick Murchison's, _Siluria_.

But as the ages rolled on, they got fewer and fewer, these Terebratulae; and now there are hardly any of them left; only six or seven sorts are left about these islands, which cling to stones in deep water; and the first time I dredged two of them out of Loch Fyne, I looked at them with awe, as on relics from another world, which had lasted on through unnumbered ages and changes, such as one's fancy could not grasp.
But you will agree that, if Master Analysis took that shell to pieces, Master Synthesis would not be likely to put it together again; much less to put it together in the right way, in which Madam How made it.
And what was that?
By making a living animal, which went on growing, that is, making itself; and making, as it grew, its shell to live in.

Synthesis has not found out yet the first step towards doing that; and, as I believe, he never will.
But there would be no harm in his trying?
Of course not.