Their food is chiefly fish, for the capture of which their
long narrow beaks, armed with numerous sharp-pointed teeth, are well
adapted, but some also devour crustaceans and molluscs. They are mostly
gregarious, and the agility and grace of their movements in the water
are themes of admiration to the spectators when a "school of porpoises"
is playing round the bows of a vessel at sea.

[Illustration: The Common Dolphin (_Delphinus delphis_).]

The type of the group is the common dolphin (_D. delphis_) of the
Mediterranean and Atlantic, which usually measures 6 to 8 ft. in length,
and is thickest near the centre, where the back fin rises to a height
of 9 or 10 in., and whence the body tapers towards both extremities. The
forehead descends abruptly to the base of the slightly flattened beak,
which is about 6 in. long, and is separated from the forehead by a
transverse depression. The mouth is armed with sharp, slightly curved
teeth, of uniform size, varying in number from forty to fifty on each
side of both jaws. The aperture of the ear is exceedingly minute; the
eyes are of moderate size and the blow-hole is crescent-shaped. The
colour of the upper surface is black, becoming lighter on the flanks,
and perfectly white below. Dolphins are gregarious, and large herds
often follow ships. They exhibit remarkable agility, individuals having
been known to leap to such a height out of the water as to fall upon the
deck. Their gambols and apparent relish for human society have attracted
the attention of mariners in all ages, and have probably given rise to
the many fabulous stories told of dolphins. Their appearance at sea was
regarded as a good omen, for although it presaged a tempest, yet it
enabled the sailors to steer for a place of safety. The dolphin is
exceedingly voracious, feeding on fish, cuttlefishes and crustaceans. On
the south coast of England it lives chiefly on pilchard and mackerel,
and when in pursuit of these is often taken in the nets. The female
brings forth a single young one, which she nurses most carefully. Her
milk is abundant and rich, and during the operation of suckling, the
mother floats in a slightly sidelong position, so as to allow of the
necessary respiration in herself and her young. The dolphin was formerly
supposed to be a fish, and allowed to be eaten by Roman Catholics when
the use of flesh was prohibited, and it seems to have been esteemed as a
delicacy by the French. Among the seafaring po