ctness from those north of the equator; and
this remark they extend to animals of all classes, from those of a more
simple to those of a more complex organization--from the sponges and
Medusae to the Cetacea. "Among all those which we have been able to
examine," say they, "with our own eyes, or with regard to which it has
appeared to us possible to pronounce with certainty, there is not a
single animal of the southern regions which is not distinguished by
essential characters from the analogous species in the northern
seas."[909]

On comparing the freshwater fish of Europe and North America, Sir John
Richardson remarks, that the only species which is unequivocally common
to the two continents is the pike (_Esox lucius_); and it is curious
that this fish is unknown to the westward of the Rocky Mountains, the
very coast which approaches nearest to the old continent.[910] According
to the same author the genera of freshwater fish in China agree closely
with those of the peninsula of India, but the species are not the same.
"As in the distribution," he adds, "of marine fish, the interposition of
a continent stretching from the tropics far into the temperate or colder
parts of the ocean, separate different ichthyological groups; so with
respect to the freshwater species, the intrusion of arms of the sea
running far to the northwards, or the interposition of a lofty
mountain-chain, effects the same thing. The freshwater fish of the Cape
of Good Hope and the South American ones, are different from those of
India and China, &c."[911]

Cuvier and Valenciennes, in their "Histoire des Poissons," observe, that
very few species of fish cross the Atlantic. Although their statement is
correct, it is found that a great many species are common to the
opposite sides of the Indian Ocean, inhabiting alike the Red Sea, the
eastern coast of Africa, Madagascar, the Mauritius, the Indian Ocean,
the southern seas of China, the Malay archipelago, the northern coasts
of Australia, and the whole of Polynesia![912] This very wide diffusion,
says Sir J. Richardson, may have been promoted by chains of islands
running east and west, which are wanting in the deep Atlantic. An
archipelago extending far in longitude, favours the migration of fish by
multiplying the places of deposit for spawn along the shores of islands,
and on intervening coral banks; and in such places, also, fish find
their appropriate food.

The flying fish are found (some straggl