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Unformatted text preview: Untitled Cambrian to the Carboniferous eras. They have no direct descendants to-day. They were jointed-footed animals, allied to Crustaceans and perhaps also to King-crabs. They were able to roll themselves up in their ring-armour.] [Illustration: _Photo: British Museum (Natural History)._ THE GAMBIAN MUD-FISH, PROTOPTERUS It can breathe oxygen dissolved in water by its gills; it can also breathe dry air by means of its swim-bladder, which has become a lung. It is a _double-breather_, showing evolution in process. For seven months of the year, the dry season, it can remain inert in the mud, getting air through an open pipe to the surface. When water fills the pools it can use its gills again. Mud-nests or mud encasements with the lung-fish inside have often been brought to Britain and the fish when liberated were quite lively.] [Illustration: THE ARCHOPTERYX (_After William Leche of Stockholm._) A good restoration of the oldest known bird, Archopteryx (Jurassic Era). It was about the size of a crow; it had teeth on both jaws; it hadEra)....
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- Fall '08