ing adaptations, namely, the seals and also the Manatee
and Dugong known as the Sirenians (so-called because they give rise to
sailors' stories of mermaids and sirens), but these are far less
changed, less modified than the whales. The whales have acquired a
completely fish-like form. They frequently have a large back fin, and
have lost the hind legs altogether. The horizontally spread flukes of
the whale's tail have nothing to do with the hind legs, whereas the
common seal's hind legs are tied together so as to form a sort of
tail. In the bigger whales, sunk deep in the muscle and blubber, we
find on each side well forward in the body (not near the tail) a pair
of isolated, unattached bony pieces, which are the hip-bone and
thigh-bone--all that remains of the hind limbs. The neck is so short
that in many whales the seven neck-bones, or "vertebrae," are all fused
into one solid piece not longer than a single ordinary vertebra, and
showing six grooves marking off the seven vertebrae which have united
into one.

The head is more strangely altered than any other part of the whale.
The jaws are greatly elongated--so as to give a beak-like form in
all--but this region is specially long and narrow in the "beaked
whales" known to zoologists by the name Ziphius, in which it consists
of a solid piece of ivory-like bone, which we find in a fossil state
in the bone-bed of the Suffolk Crag. Farther back the bones of the
face are suddenly widened in all whales and porpoises, and in many
these bones grow up into enormous crests and ridges. The nostrils,
instead of being placed, as in other animals, at the free end of the
snout or beak, lie far back, so as to form the "blow-hole," which is
near the middle of the head.

The circulation of the blood and the breathing of whales (including in
that term the smaller kinds known as dolphins and porpoises) is still
a matter which is not properly understood. When a Greenland whale is
struck by the harpoon it dives vertically downward to a depth of 400
fathoms and more (nearly half a mile), and occasionally wounds the
skin and bones of its snout by violently striking it on the
sea-bottom. It remains below as long as forty minutes. Physiologists
wish to know how the sudden compression of the air in the lungs in
plunging to this depth and the equally sudden expansion of it in
rising from such a depth is dealt with in the whale's economy, so as
to prevent the absolutely deadly results which woul