THE DOUBLE-BREATHERS 251

the upper lip longer than the lower, and the tail is
heterocercal—that is, it has one lobe larger than the
other, the backbone extending into the larger lobe—
altogether, this voracious pike is just such a fish as
one would expect to find swimming out of a-sand-
stone bed. The sturgeons are much more lightly
protected, their armour being represented by de-
tached dermal plates of true bone. It is generally
admitted that the bony fishes were derived from the
ganoids through certain extinct forms.

PIPNOI—This is another order with a long
pedigree, one of its genera (Ceratodus) having per-
sisted up to now since Permian times. Their teeth
are remarkable for consisting of merely a pair of
large molars in both jaws, and a pair of vomerine
teeth ; but the main characteristics of the order are the
amphibian nature of the heart, and the fact that the
swim-bladder acts as a single or double lung; in
short, the dipnoi, in many respects, clearly foreshadow
the amphibians. The barramunda (Ceratodus For-
stert) has red flesh, like a salmon, and is often called
the Dawson salmon, from having been found in the
Queensland river of that name. It is a curious-
looking fish, almost oblong in shape, with short, eel-
like tail and flipper-like lower fins, the fore-pair being
close up to the gills) The other genera are the
somewhat common African Protopterus, of which
there are living examples in the Reptile House at the
London Zoological Gardens, and the Lepilosiren of
the Amazon, one of the rarest and most ancient-
looking of modern fishes. Ceratodus, as we have