They are mere live bags full of jelly, which can take almost any shape they like, and thrust out arms--or what serve for arms--through the holes in their shells, and then contract them into themselves again, as this Globigerina does.

What they feed on, how they grow, how they make their exquisitely-formed shells, whether, indeed, they are, strictly speaking, animals or vegetables, Analysis has not yet found out.

But when you come to read about them, you will find that they, in their own way, are just as wonderful and mysterious as a butterfly or a rose; and just as necessary, likewise, to Madam How's work; for out of them, as I told you, she makes whole sheets of down, whole ranges of hills.
No one knew anything, I believe, about them, save that two or three kinds of them were found in chalk, till a famous Frenchman, called D'Orbigny, just thirty years ago, told the world how he had found many beautiful fresh kinds; and, more strange still, that some of these kinds were still alive at the bottom of the Adriatic, and of the harbour of Alexandria, in Egypt.
Then in 1841 a gentleman named Edward Forbes,--now with God--whose name will be for ever dear to all who love science, and honour genius and virtue,--found in the AEgean Sea "a bed of chalk," he said, "full of Foraminifera, and shells of Pteropods," forming at the bottom of the sea.
And what are Pteropods?
What you might call sea-moths (though they are not really moths), which swim about on the surface of the water, while the right-whales suck them in tens of thousands into the great whalebone net which fringes their jaws.

Here are drawings of them.

1.