Oliver Wendell Holmes, The Poet at the Breakfast Table, Boston, Houghton, 1872, p. 229.

Yes, -he said,- I have a kind of notion of the way in which Library ought to be put together- no, I don’t mean that, I mean ought to grow. I don’t pretend to say that mine is a model, but it serves my turn well enough, and it represents me pretty accurately. A scholar must shape his own shell, secrete is only separation, you know, of certain elements derived from the materials of the world about us. And a scholar’s study, with the books lining its walls, is his shell. It is n’t a mollusk’s shell, either ; it ‘s a caddice-worm’s shell. You know about the caddice-worm?
-More or less ; less rather than more,- was my humble reply.
Well, sir, the caddice-worm is the larva of a fly, and he makes a case for himself out of all sorts of bits of everything that happen to suit his particular fancy, dead or alive, sticks and stones and small shells with their owners in’em, living as comfortable as ever. Every one of these caddice-worms has his special fancy as to what he will pick up and glue together, with a kind of natural cement he provides himself, to make his case out of. In it he lives, sticking his head and shoulders out once in a while, that is all. Don’t you see that a student in his Library is a caddice-worm in his case ? I’ve told you that I take an interests in pretty much everything, and don’t mean to fence out any human interest from the private grounds of my intelligence.