<DIV>Works of art disappear, species are extinguished, books are lost, cities drown, things once thought immortal suddenly aren't there at all. Whole libraries of knowledge, and whole galleries of secrets are gone. Our culture, our knowledge, and all our lives are shadows cast by what went before. We are defined, not by what we have, but by what we have lost along the way. <I>Lost Worlds </I>is a glossary of the missing, a cabinet of absent curiosities. No mere miscellany, it weaves a web of everything we no longer have. Michael Bywater,<I> </I>"Lost Worlds" columnist for the <I>Independent on Sunday,</I> teaches at Cambridge University.</DIV>