more important, rendering the processes of development among animals
one of the most interesting and instructive studies to which the
naturalist can devote himself, in the present state of his science.
The accuracy of this test, not only as explaining the relations
between animals now living, but as giving the clew to their connection
with those of past times, cannot but astonish any one who makes it the
basis of his investigations. The comparison of embryo forms with
fossil types is of course difficult, and must in many instances be
incomplete, for while, in the one case, death and decay have often
half destroyed the specimen, in the other, life has scarcely stamped
itself in legible characters on the new being. Yet, whenever such
comparisons have been successfully carried out, the result is always
the same; the present representatives of the fossil types recall in
their embryonic condition the ancient forms, and often explain their
true position in the animal kingdom. One of the most remarkable
examples of this in the type we are now considering, is that of the
Comatula already mentioned. Its condition in the earlier stages of
growth, when it is provided with a stem, at once shows its relation to
the old stemmed Crinoids, the earliest representatives of the class of
Echinoderms.
These coincidences are still more striking among living animals, where
they can be more readily and fully traced, and often give us a key to
their relative standing, which our knowledge of their anatomical
structure fails to furnish. This is perhaps nowhere more distinctly
seen than in the type of Radiates, where the Acalephs in their first
stages of growth, that is, in their Hydroid condition, remind us of
the adult forms among Polyps, showing the structural rank of the
Acalephs to be the highest, since they pass beyond a stage which is
permanent with the Polyps; while the adult forms of the Acalephs have
in their turn a certain resemblance to the embryonic phases of the
class next above them, the Echinoderms. Within the limits of the
classes, the same correspondence exists as between the different
orders; the embryonic forms of the higher Polyps recall the adult
forms of the lower ones, and the same is true of the Acalephs as far
as these phenomena have been followed and compared among them. In the
class of Echinoderms the comparison has been carried out to a
considerable extent, their classification has hitherto been based
chiefly upon the ambulacral system, so characteristic of the class,
but so unequally developed in the different orders. This places the
Holothurians, in which the ambulacral system has its greatest
development, at the head of the class; next to them come the
Sea-urchins or Echinoids; then the Star-fishes; then the Ophiurans and
Crinoids, in which the ambulacral system is reduced to a minimum.
Another basis for classification in this type, which gives the same
result, is the indication of a bilateral symmetry in some of the
orders. In the Holothurians, for instance, there is a decided tendency
toward the establishment of a posterior and anterior extremity, of a
right and left, an upper and lower side of the body. In the
Sea-urchins, in many of which the mouth is out of centre, placed
nearer one side than the other, this tendency is still apparent, while
in the three lower groups, the Star-fishes, Ophiurans, and Crinoids,
it is almost entirely lost, in the equal division of identical parts
radiating from a common centre. A comparison of the embryonic and
adult forms in these orders, confirms entirely this classification
based upon structural features. The Star-fishes, in their earlier
stages, resemble the mature Ophiurans, while the Crinoids, the lowest
group of all, retain throughout their whole existence many features
characteristic of the embryonic conditions of the higher Echinoderms.
In this principle of classification, already so fertile in results, we
may hope to find, in some instances, the solution of many perplexing
points respecting the structural rank of animals, the confirmation of
classifications already established; in others, an insight into the
true relations of groups which have hitherto been divided upon purely
arbitrary grounds.
* * * * *
DISTRIBUTION OF LIFE IN THE OCEAN.
We have seen that while our bay is rich in certain species, it is
wholly deficient or but scantily supplied with others, and that the
character of the animals inhabiting its waters is more or less
directly connected with general physical conditions. Such an area,
limited though it be, gives us some insight into the laws which, in
their wider application, control the distribution of marine life along
the shores of the most extensive continents. The coast of
Massachusetts, taken as a whole, is like that of New England
generally, a rocky coast; yet it has its sandy and muddy beaches, and
though it lies for a great part open to the sea, it has nevertheless
its sheltered harbors, its quiet bays and snug recesses.
A comparison of these limited localities with far more extensive
reaches of shore, where similar physical conditions prevail, shows
that they reproduce, in fainter and less various characters of course,
in proportion to their narrower boundaries, but still with a certain
fidelity, the same combinations of animal and vegetable life. In other
words, a sandy beach, however small, gives us some idea of the nature
of the animals we may look for on any sandy coast, as, for instance,
clams of various kinds, razor-shells, quahogs, snails, &c., creatures
who can penetrate the sand, drag themselves through it or over it,
leaving their winding trails as they go, and to whom the conditions
prevailing in such spots are genial. So the narrowest mud flat on the
sea-shore or muddy beach will give us the same dead and inanimate
aspect which characterizes a more extensive coast of like character,
where the gases always generated in mud are deadly to many kinds of
animals. The beings who find a home in such localities are of closely
allied species, chiefly a variety of worms, who burrow their way into
the mud, and seem to court the miasma so fatal to other creatures. The
same is true of any stony beach or rocky shore not more than a quarter
of a mile in length; it gives us an idea of the animal population on
any similar coast of greater extent.
These correspondences are of course modified by differences in
climatic conditions. The animals on a sandy beach or a rocky shore, on
the coast of Great Britain, for instance, are not absolutely identical
with those of a sandy beach or a rocky shore on the coast of New
England, but they are more or less nearly related to them. Naturalists
refer to this reiteration, all the world over, of like organic
combinations under similar circumstances, when they speak of
"representative species." The aggregate result is the same, though the
individual forms are slightly modified. And here lies one secret of
the infinite variety in nature, by which the old seems ever new, and
the same thought has an eternal freshness and originality, endlessly
repeated, yet never hackneyed.
In this sense our bay presents, on a miniature scale, a variety of
physical and organic combinations, which may be compared to those more
extensive divisions in the geographical distribution of animals and
plants, called by naturalists zoölogical or botanical provinces or
districts, the animal and vegetable populations of which are
technically designated as their faunæ and floræ. Such organic realms,
as we may call them, have long been recognized on land, and the most
extensive among them are easily distinguished. No one will fail to
recognize the tropical zone, with its royal dynasty of palms and all
the accompanying glories of a tropical vegetation, its birds of
brilliant plumage, its large Mammalia, lions, tigers, panthers,
elephants, and its great rivers haunted by gigantic reptiles. Nor is
the representation of vegetable and animal life less characteristic in
the temperate zone, where the oak is monarch of the woods, with all
his attendant court of elms, walnuts, beeches, birches, maples, and
the like, where birds of more sober hues, but sweeter voices, take the
place of the brilliant parrots and many-tinted humming-birds of the
tropical forest; while buffaloes, bears, wolves, foxes, and deer
represent the larger Mammalia. In the arctic zone, though marked by
peculiar and distinctive features, vegetation has dwindled to a
minimum; the birds are chiefly gulls and ducks, which go there for the
breeding season in the summer, and the reindeer and polar bears are
almost sole possessors of the snow and ice-fields; but this meagreness
in the representation of the larger land Mammalia is amply compensated
in the numbers of heavy aquatic Mammalia, the whales, walruses, seals,
and porpoises of the Arctic seas.
During the last half-century, since the geographical distribution of
animals and plants has become a subject of more careful investigation
among naturalists, these broad zones of the earth's surface, with
their characteristic populations and vegetation, have been subdivided,
according to more limited and special combinations of organic forms,
into narrower zoölogical and botanical areas. The application of these
results to marine life is however of much more recent date, and indeed
it would seem at first sight, as if the water, from its own nature,
could hardly impose a barrier so impassable as the land. The
localization of the marine faunæ and floræ is nevertheless as distinct
as that of terrestrial animals and plants, and late investigations
have done much to explain the connection of this distribution with
physical conditions.
A glance at the coast of our own continent, starting from the high
north and making the circuit of its shores, from Baffin's Bay to
Behring's Straits, will show us to what a variety of physical
influences the animals who live along its shores are subjected. On the
shores of Baffin's Bay, especially on the inner coast of Greenland,
where the glaciers push their way down to the very brink of the water,
and annually launch their southward-bound icebergs, we shall hardly
expect to find a very abundant littoral fauna. On its western shore,
where the ice does not advance so far, and a greater surface of rock
is exposed, the circumstances are more favorable to the development of
animal life. Here abound the winged Mollusks (Pteropods), often swept
down to the coast of Nova Scotia by the cold current from Baffin's
Bay; the "whale feed," as the fishermen call them, because the whales
devour them voraciously. Here occur also many compound Mollusks,
especially a variety of Ascidians, and the highly colored stocks of
Bryozoa. With them is found the Comatula of the northern waters, one
of the few modern Crinoids, and beside these a number of Star-fishes,
Sea-urchins, and Holothurians, not differing so essentially from those
already described as to require special mention.
Along the shore of Labrador and Newfoundland, the coast is wholly
rocky, and especially about Newfoundland it is deeply indented with
bays. Here there is ample opportunity for the growth of certain kinds
of animals in sheltered nooks. The number of species is, however, much
greater along the shores of Maine, Nova Scotia, and New Brunswick than
in Labrador, owing no doubt to the milder climate. The beautiful shore
of Maine, with its countless islands, and broken, picturesque outline,
is very rich in species. Parts of this coast are remarkable for a
variety of naked Mollusks, as well as for the great numbers of
bright-colored Actiniæ, and also for the more brilliant kinds of
Holothurians, the Cuvieria, and the like. The latter are especially
abundant in the Bay of Fundy, and here also occurs the only Northern
representative on our coast of the Sea-fans or Gorgoniæ, so common on
the shores of Florida.
Farther south, from Cape Cod to Cape Hatteras, the character of the
coast changes; it becomes more sandy, and though here and there the
aspect is varied by a rocky promontory or a stony beach, yet the
general character is flat and sandy. With this new character of the
shore, the fauna is also greatly modified, and it is worthy of remark,
that while thus far the representative species have reflected the
character of animals to the north of them, they now begin to represent
rather those of the Carolina shores. South of Cape Cod come in a kind
of Scallop and Periwinkle, very different from the larger Scallops
found on the coast of Maine and the British Provinces; our Sea-urchin
is replaced by the Echinocidaris, with its few long spines, and an
entirely new set of Crustacea and Worms make their appearance on this
more sandy bottom. And here we must not forget that not only is the
aspect of the animal life changed, as we pass from a rock-bound to a
sandy coast, but that of the vegetation also. The various many-tinted
sea-weeds of the rocky shore disappear almost entirely, and their
place is but poorly supplied by the long eel-grass, which is almost
the only marine plant to be found in such a locality. Beside its more
sandy character, the coast from Cape Cod to Cape Hatteras is affected
by the large amount of fresh water poured into the sea along its whole
line, greatly modifying the character of the shore animals. The
Hudson, the Delaware, the Susquehanna, the Potomac, the James, the
Roanoke, and the large estuaries connected with some of these rivers,
give a very peculiar character to the shore, and bring down, not only
a vast supply of fresh water, but also a large quantity of detritus of
all sorts from the land. Under these circumstances life would be
impossible for many of the animals which live farther north. The only
locality on the North Atlantic shore, where the conditions are
somewhat similar, is at the mouth of the St. Lawrence, that great
drainage-bed through which the Canadian lakes empty their superfluous
waters into the Gulf of St. Lawrence.
The whole coast of the Carolinas, from Cape Hatteras to Florida, is a
sandy beach; but though in this respect it resembles that immediately
to the north of it, it differs greatly in other features.
Comparatively little fresh water is poured into the ocean along this
shore, and its more southerly range, instead of being protected by
sand-spits like Pamlico and Albemarle Sounds, or broken by estuaries
and inlets like the coast of Virginia, lies broadly open to the sea.
On its extensive beaches we have the large Pholas, burrowing deep
below the surface, and the Cerianthus, those long, cylindrical
Actiniæ, enclosed in sheaths, with their bright crowns of
gayly-colored tentacles; the free colonies of Halcyonoids abound also
on this coast, and a new set of Sea-urchins (Spatangoids and
Clypeastroids) make their appearance.
Farther south, along the Florida coast, a new element comes in, that
of the coral reefs, enclosing shallow channels near the shore, and
thus providing sheltered harbors on their leeward side, while on their
seaward side they slope steeply to the ocean. Beside this, the reef
itself affords a home for a great variety of creatures, who bore their
way into it and live in its recesses, as some insects live in the bark
of trees. Perhaps a more favorable combination of circumstances for
the development of marine life does not exist anywhere than about the
coral reefs of Florida, and certainly nowhere is there a more rich and
varied littoral fauna, especially on their western shore within the
Gulf of Mexico. Here swims the Portuguese Man-of-War, borne gayly
along on the surface of the water by its brilliant float, here the
blue Velella sets its oblique sail to the wind, and hosts of the
lighter and more brightly tinted corals fringe the shore with a
many-colored shrubbery. In these waters are also found the blue and
yellow Angel-fish, the Parrot-fish (Scarus), and the strange
Porcupine-fish (Diodon). Vegetable life is comparatively scanty in
these tropical waters, where there are scarcely any sea-weeds, except
the corallines or limestone Algæ of the reefs. The shore of the Gulf
of Mexico, as a whole, has much the same character as that of the
Carolinas, until we reach the point where the mountains and plateau of
Mexico come down to the coast. From this point to the Isthmus of
Panama the coast is again rocky.
Crossing the Isthmus and following the Pacific shore of the continent
northward, we find a sandy open shore alternating with rocky beaches
as far north as Acapulco. Along this coast there is to be found a
great variety of corals, especially Sea-fans, growing on the rocks,
but no reef. The Pocillopora, an Acalephian coral, the Pacific
representative of the Millepore of Florida, is especially abundant. On
the peninsula of Lower California we come again upon a rocky coast,
with steep bluffs, extending into the sea. Within the Gulf of
California are found, on its sandy coast, peculiar kinds of
Sea-urchins, Spatangoids, and Clypeastroids, which occur nowhere else
on this coast. From Cape St. Lucas up to the Straits of Fuca, with the
exception of the large estuary forming the Bay of San Francisco, there
are scarcely a couple of harbors of any consequence. The whole shore
is most inhospitable, and the violent northwest winds in summer, and
the southeast winds in winter, render it still more bleak and
difficult of approach. In consequence of these conditions, the fauna
is scanty along a great part of the shore; the best spots for
collecting are the beaches, near the head of the peninsula, opposite
the islands of Santa Barbara and San Diego, and that within the harbor
of San Francisco. On the former, large Craw-fishes abound (Palinurus),
akin to those of Florida, though specifically different from them. In
the latter, the great amount of fresh water prevents the fauna from
being exclusively marine; this harbor is, nevertheless, the great
centre of the viviparous fishes, and contains also a large variety of
peculiarly shaped Sculpins.
Farther north, between the Straits of Fuca and the island of Sitka,
the shore resembles that of Maine, with its many islands, bays, and
inlets; a succession of long, narrow islands forms a barrier along the
coast, enclosing the shore waters, so as almost to make them into an
inland sea. But little fresh water empties upon this part of the
coast, and here, where the salt water is little modified by any
deposit from the land, but where the violence of the ocean is broken
by this barrier of islands, there is a full development of marine
life. The shores of the Gulf of Georgia, and those of Vancouver's
Island, seem to be especially the home of the Star-fishes. The fauna
of this locality has been but little investigated, and yet the number
of species of Star-fishes known from there is greater than from any
other region; many of them are of colossal size, measuring some four
feet in diameter. This coast seems also very favorable for the
development of Hydroids, in consequence of which its waters swarm with
a variety of Jelly-fishes. The Pennatula, that pretty compound
Halcyonoid, with its feather-like sprays, is another characteristic
type of this fauna. Beyond this, from Sitka to Behring's Straits, the
same rocky coast prevails as in Labrador and Greenland. In Behring's
Straits we return again to the forests of beautiful compound Mollusks,
or rather to a variety of "representative species," resembling the
Bryozoa and Ascidians so abundant in Baffin's Bay. The depth of the
water, however, is much less here than on the corresponding Atlantic
coast, where, south of Greenland, along the shore of Labrador, the
water is very deep, while in Behring's Straits the depth is not
greater than from one hundred to one hundred and twenty fathoms. The
respective faunæ of these two shores are also affected by the
difference of temperature, the cold current from Baffin's Bay sweeping
down upon the coast of Labrador, while, through Behring's Straits, the
warm current from the Pacific pours into the Arctic Ocean.
Thus the whole coast of our continent is peopled more or less thickly
with animals. But now arises a new set of inquiries; how far into the
sea do these animals extend? how wide is their domain? Do they wander
at will in the ocean, or are they bound by any law to keep within a
certain distance of the shore? These questions would seem to be easily
answered, for wherever we go on the surface of the sea, and as far as
the eye can penetrate into its depths, we find it full of life; and
yet a closer examination shows that all these beings have their
appointed boundaries. Along the shores, animal and vegetable life
seems to be distributed in certain definite combinations. Those who
are familiar with rocky beaches readily recognize the different bands
of color produced by the various kinds of sea-weed growing at given
distances between high and low-water-mark. First comes the olive green
rockweed (the Fucus), and with it are found barnacles and small
Crustacea, myriads of which are to be seen hopping about in this
rockweed when the tide is out. Below these are the brown crispy
Rhodersperms and Melanosperms, and associated with them are
Star-fishes, Crabs, and Cockles. Next in order is the Laminarian zone.
Here we have the broad fronds of the Laminaria, the "devil's aprons,"
as the fishermen call them; in this zone is the home of the
Sea-urchin, and here will be found also a few small fishes. Lastly we
have the Coralline zone, so called on account of the lime deposit in
the sea-weeds, giving them the rigidity of corals; among these the
Lobsters make their appearance, and here are to be found also numerous
clusters of Hydroids, the nurses of the Jelly-fishes.
This distribution is not casual; these belts of animal and vegetable
life are sharply defined and so constantly associated, that they must
be controlled by the same physical laws. The first important
investigations on this subject were made by Örsted, the distinguished
Danish naturalist. He undertook a complete topographical survey of the
coast near which he lived, carrying his soundings to a depth of some
twelve fathoms, and found that both the fauna and flora of the shore
were divided, according to the depth of the water, into bands of
vegetable and animal life, corresponding very nearly with those given
above. His observations were, however, limited, not extending beyond
the neighborhood of his home. It is to Edward Forbes, the great
English naturalist, whose short life was so rich in results for
science, that we owe a more complete and extensive investigation of
the whole subject.
[Illustration: Diagram of a rocky beach.]