surface of water are removed from the influence of atmospheric oxygen,
and that they form exceptions to this law. But such is not the case, for
water absorbs and holds in solution a certain quantity of air, the
oxygen of which is taken up by aquatic animals. In the lower forms of
animals inhabiting water, the absorption of this vital element takes
place at the general surface of the body; but in the more highly
organized creatures there are special organs appropriated to this
purpose, of which the gills of a fish may be cited as a typical example.
The giving out of carbonic acid is an action as universal in the animal
world as the absorption of oxygen, and all aquatic animals tend to
charge the water in which they live with this gas. Fish, or any other
water animals, will soon die if they are placed in water from which all
the air has previously been expelled by boiling, or by placing under the
receiver of an air-pump. In this case the creature dies from want of
oxygen; but it would also die, even if supplied with oxygen, were the
poisonous carbonic acid emitted by itself allowed to accumulate in the
liquid. In nature, this carbonic acid forms the food of aquatic plants
and sea-weeds, and these restore oxygen to the water. If a bunch of
watercresses be placed in a bottle filled with water, and exposed to
strong sunshine, the leaves may soon be seen covered with small bubbles
of gas. This gas may be collected and examined by a suitable arrangement
of the bottle, and it will be found to be pure oxygen.
The merit of having first imitated the plan of nature for the
preservation of aquatic animals appears to belong to Mr. Ward, the
inventor of the “Wardian cases” for ferns and other plants. He, in 1841,
formed in London a fresh-water aquarium, in which, for the first time,
the animals were kept in a healthy condition by the compensating action
of plants. Mr. Gosse, Dr. Price, and others, made experiments with
marine animals and plants, about 1850. Mr. Mitchell, who was then
secretary to the Zoological Society of London, saw about this time a
small aquarium on the balancing principle at Dr. Bowerbank’s, and this
suggested the erection of the fish-house in the Zoological Gardens,
Regent’s Park. This was opened in 1853, being the first public aquarium
ever constructed. The tanks remain at the present time in nearly their
original condition, and this aquarium has been remarkable, not only as
predecessor of the many public aquaria which have since been erected,
but for having given rise to a movement in favour of aquaria as domestic
establishments. The setting-up of household aquaria became almost the
rage of the day, and so many books and magazine articles devoted to the
subject appeared during the ten years following the establishment of the
Regent’s Park aquarium, that the literature of the subject is quite
considerable. Mr. Gosse showed how water for marine aquaria could be
produced by adding to fresh water the solid constituents of sea-water;
and, in the marine aquaria of some inland towns far distant from the
sea, this artificial sea-water is the only kind used. After the
establishment of the Regent’s Park aquarium, public aquaria were opened
successively in Dublin, Galway, Edinburgh, Scarborough, Weymouth, the
Crystal Palace, Brighton, Manchester, and Southport; and on the
continent at Paris, Hamburg, Hanover, Boulogne, Havre, Brussels,
Cologne, Vienna, and Naples; also in North America at San Francisco, and
in other places. The general interest in public aquaria, and especially
marine aquaria on the large scale, seemed to increase as the comparative
failure of the domestic tanks lessened the taste for them. The causes of
the failure so often attending the attempt to maintain aquaria on the
small scale arise partly from the amateur naturalist’s want of exact
knowledge, and the great amount of attention and care required, and
partly from the inherent difficulties of the subject. An aquarium, even
on the largest scale, and with every appliance that science can suggest,
only represents, after all, _a few_ of the conditions which actually
exist in nature; but in small vessels, with a limited quantity of water,
without the continual motion of the liquid, which belongs naturally to
seas and streams, and with circumstances of light and temperature widely
different from those which are obtained in nature, it is not surprising
that the success of domestic aquaria should be but very partial, and
that the taste for them should have declined accordingly.
Many public aquaria proved commercial failures; but we select for
special description two which have been thoroughly efficient, and are
remarkable for size, reputation, and successful management. The
arrangements at these two institutions as regards the aëration and
renewal of the water are, however, quite different. Some plan by which
the same sea-water might be supplied with oxygen, and kept in a clear
and pure condition, was necessary for the very existence of the inland
marine aquarium at the Crystal Palace, whereas the position of Brighton
made the natural sea-water more available. The success of the former
method at the Crystal Palace Aquarium, under the judicious system
adopted by Mr. W. A. Lloyd, the superintendent, perhaps renders this
aquarium one of the most interesting, in a scientific point of view, of
any yet in operation. The water here is never changed by the addition of
sea-water; but fresh water is added as required, simply to supply the
loss by evaporation; and any solid constituents which the animals may
abstract from the water as material for their shells is replaced, so
that the ordinary composition of sea-water is maintained. This is merely
imitating Nature, for the evaporation from the surface of the sea is
compensated by the fall of rain and the influx of rivers, the latter
constantly bringing in the various salts held in solution. The following
particulars regarding the Crystal Palace Aquarium are derived from Mr.
Lloyd’s excellent handbook, which contains not only clear descriptions
of the inhabitants of the tanks, but interesting historical notices and
a well-written disquisition on the principles which should regulate the
construction and management of aquaria.
_THE CRYSTAL PALACE AQUARIUM._
The building was commenced in July, 1870, and was opened in August,
1871. It was designed by Mr. Driver, of Victoria Street, and presents an
admirable simplicity, which entirely accords with the purpose for which
it was erected. The whole available space has been occupied, and nothing
has been wasted on unmeaning or fantastic embellishments. Even the
decorative shams, in which ordinary painters delight, have been
excluded. No part of the walls or of the woodwork is painted to look
like marble, or even to imitate oak. The building, which is about 400
ft. long and 70 ft. broad, is situated at the north end of the Palace,
partially occupying the site of the portion which was so unfortunately
burnt down in 1866. It is but one storey high, and besides a large
reservoir beneath the floor, holding 100,000 gallons of sea-water, there
is a series of sixty tanks, with thick plate-glass fronts, which
collectively contain 20,000 gallons of water. This water, weighing over
1,000,000 lbs., was brought from the coast and conveyed to the Palace by
the Brighton Railway Company at a very moderate rate. For many weeks
after the water was placed in the reservoir and tanks it was very
turbid, from taking up the lime used in their construction and in that
of the rockwork. In this condition it was very alkaline; but the lime
was slowly precipitated by the carbonic acid of the air, the water
became clear, and vegetation appeared in the tanks. The great capacity
of the reservoir facilitates the cleansing of the water; for, supposing
that the water in one of the tanks, holding, say, 6,000 gallons, became
turbid from any cause, the water from this tank could be run off into
the reservoir, where its mixture with the much larger quantity would not
sensibly affect the purity of the mass, from which within half an hour
the tank could again be filled.
All the tanks are constantly receiving water from the clear and cool
reservoir below, in which there are no animals, so that the motion of
the water in the tanks, like that of the ocean, is incessant. The water
issues from the pump at a rate (indicated by a counter) of from 5,000 to
7,000 gallons per hour. The pump is worked by a steam engine of three
horse-power, and the machinery requires the unremitting attention of
three engineers, who succeed each other by turns, each working for eight
hours. Two sets of the machinery—pumps, steam engines, and boilers—are
provided, one being always kept in reserve, ready for use in case of any
accident. Even in winter, when, from the lower temperature, the water
contains the largest amount of oxygen, it is found that the stopping of
the circulation of the water for only a few hours occasions manifest
discomfort to some of the animals. The water is poured into the two
centre tanks in an equally divided stream, and by a simple fall of a few
inches from tank to tank it flows by two routes to the lowest tank, from
which it passes into the reservoir below. This incessant circulation of
the water constantly exposes fresh surfaces to the action of the air, by
which oxygen is absorbed. But besides this, other small streams of water
are made to forcibly enter the tanks from jets, by which a large
quantity of air is carried down in very small bubbles. The removal of
carbonic acid is accomplished by the vegetation which spontaneously
makes its appearance in sea-water under suitable circumstances. It has
been found quite unnecessary to introduce purposely any kind of
sea-weeds, for the spores of low forms of vegetation are always present
in the water, and they develop rapidly under the stimulus of light.
Indeed, one of the difficulties of aquarium management is to avoid this
excessive vegetation by limiting the light as much as possible, and yet
leave sufficient illumination for the observation of the animals. The
amount of light falling upon each tank is very carefully attended to at
the Crystal Palace, and where it cannot be diminished sufficiently to
check the overgrowth of vegetation, without at the same time interfering
with a proper view of the animals, certain molluscs and fishes which
live upon _algæ_ are put into the tanks to consume them. This
spontaneous vegetation is so vigorous that a comparatively small
quantity suffices to remove from the water all the carbonic acid which
it may derive from the animals and decomposing matters.
It should be mentioned that at this aquarium the water is never
filtered, but its clearness is obtained merely by the perfect system of
circulation. The unused food and excrementitious matters are oxygenated
by the air which the water abundantly holds in solution—thanks to the
surface exposed in its constant circulation, the injection of the jets
of water carrying minute bubbles of air into the mass of water, and the
gas given off by the vegetation. The whole process of purification is
therefore chemical, and the success and excellent adaptation of the
system may be judged from the fact that the water seen in masses 9 ft.
deep appears perfectly clear and bright. The building is very cool in
summer: even in extremely hot weather the temperature of the air within
it is never higher than 68° F., and that of the water in the tanks never
exceeds 63°. In winter the temperature of the air is maintained by
hot-water pipes at from 60° to 65°, and the temperature of the water at
about 55°. On winter evenings the aquarium is illuminated with gas, and
the habits of many nocturnal animals can then be conveniently studied.
[Illustration:
FIG. 321.—_The Opelet_ (_Anthea cereus_).
]
“All the animals in this aquarium,” says Mr. Lloyd, “have to be fed
constantly; and as for the sea-anemones—of which there are in the
aquarium over 5,000 individuals—every one of them has a morsel of food
proportioned to its size, and according to the condition of the water,
given it at frequent intervals with a pair of wooden forceps by an
attendant who makes this his sole occupation—as these flower-like
creatures, being so non-locomotive as to be almost absolutely fixed,
cannot pursue their food, or in an aquarium obtain it in any other
manner. They are here deprived of the action of the waves, which in the
actual ocean brings them nutriment, which is arrested by their outspread
and waving tentacles. The food consumed by a few of the animals now
present in the aquarium is vegetable, consisting of green weeds (_Ulva_,
_Porphyra_, _Enteromorpha_, _&c._), but by far the greater number have
animal food given them. This consists of shrimps, alive or dead, crabs,
mussels, oysters, and fish, but they are never fed on butcher’s meat.”
The creatures known as “sea-anemones” are well represented in the
Crystal Palace Aquarium. The observer cannot fail to be struck by their
resemblance to flowers, from the radiated arrangement of their
tentacles, and the beautiful colours they often exhibit. The opelet
(_Anthea cereus_), Fig. 321, is perhaps the most beautiful among British
species, and is a conspicuous denizen of the Aquarium, where its long
green tentacles, tipped with lilac, are commonly seen expanded or
twisting about like so many snakes. These tentacles are stretched out in
search of food, and when by chance an unlucky shrimp or other suitable
prey merely touches a tentacle, it is seized and held with remarkable
pertinacity, the rest of the tentacles closing round it. The mouth of
the creature, placed in the centre of the disc, then expands to an
extraordinary size, and the prey is quickly lodged in the capacious
digestive sac of the _actinia_, where the soft parts are soon dissolved,
and the hard indigestible residue is ejected by the mouth. The tentacles
of _Anthea_, and of other species belonging to the same subdivision of
the animal kingdom, are furnished with an immense multitude of curious
organs, which consist of cells or minute bags, containing coiled up
within them a slender highly elastic filament. When these cells are
compressed, the filament shoots out of its capsule to a surprising
length; and it has been supposed that the adhesive power of the
tentacles depends upon these filiferous capsules; while it is not
improbable that some virulent fluid is also emitted from the cells, for
the victims appear as if paralysed almost as soon as they are seized.
Our knowledge of these animals has been largely extended by the
opportunities of observing their habits which are afforded by marine
aquaria.
[Illustration:
FIG. 322.—_The Viviparous Blenny_ (_Zoarces viviparus_).
]
To obtain the variety of animals requisite for stocking a public
aquarium is by no means an easy matter; for the animals must be good
specimens, in a healthy condition, uninjured by their capture or
transport from the sea. The Crystal Palace Aquarium Company have at
Plymouth a large pond, which communicates with the sea at every tide;
and this, under the superintendence of the company’s resident agent,
serves as a store for animals. Similar arrangements exist at Southend,
Weymouth, Tenby, and other places. The specimens are brought to Sydenham
by fast trains—special facilities being afforded by the railway
companies for this purpose. The mode of carrying the animals depends
upon their nature, and is sometimes a matter of no little difficulty.
All fishes, except perhaps eels and blennies, must be carried in a
sufficient bulk of water; and then the due oxygenation of the water and
the removal of the carbonic acid can be but very imperfectly
accomplished. A considerable mass of water is absolutely necessary in
such cases, and the difficulties and cost of the transit are much
increased by its weight. In warm weather the quantity of oxygen retained
in the water is materially diminished, and under such circumstances the
creatures would soon perish. On the other hand, in very cold weather the
temperature may be so far reduced below that suited to their habits that
death may also result from this cause. Crabs, lobsters, sea-anemones,
sea-urchins, and similar animals can in general be carried without being
immersed in a mass of water. These animals are placed in layers of wet
sea-weed contained in baskets, so that the air has access to the
moisture which covers the bodies of the animals, which is prevented from
drying up by the humidity. As in this case the small quantity of water
exposes a very large surface to the air, oxygen is plentifully supplied.
Mr. Lloyd points out that it is owing to the readiness with which mere
films of water are aërated, that it has been found possible to convey to
Australia the eggs of salmon and trout, and hatch them there. They could
not have been carried in water, but they were successfully conveyed when
surrounded by a cool and very moist atmosphere. This mode of
transmission is much more economical and convenient than the plan of
carrying the creatures in water, and it is therefore resorted to
whenever the organization of the animal permits.
[Illustration:
FIG. 323.—_The Lancelet_ (_Amphioxus lanceolatus_).
]
Specimens of a very remarkable creature are, or lately were, exhibited
at this aquarium in the lancelet (_Amphioxus lanceolatus_), Fig. 323,
which animal itself is a comparatively recent discovery. It is about 2½
in. long, and although it is fish-like in form, it presents so many
points of structure common to lower animals, that it is looked upon by
naturalists as a link between the molluscs and the fishes—being the
lowest of the latter in organization. The creature can hardly be said to
possess a skeleton, the tissues representing that structure are so soft.
It has no definite brain, but it possesses olfactory and optic organs of
a rudimentary kind.
_THE BRIGHTON AQUARIUM._
The Brighton Aquarium, already so well known as a place of popular
resort, is a structure of considerable architectural pretensions, and is
the largest establishment of the kind in existence. The idea of this
undertaking appears to have originated with Mr. E. Birch, the engineer
of the actual structure, who, having, in 1866, visited the aquarium at
Boulogne, perceived that the construction at Brighton of a marine
aquarium on a very extended scale offered every promise of commercial
success. The promoters, in 1868, obtained from Parliament an act
authorizing them to acquire a certain site for the aquarium, but
imposing such limits as to the height of the structure that it was
necessary to place the greater part of the building below the level of
the ground, a matter involving considerable engineering difficulties.
The aquarium is situated close to the Chain Pier and immediately below
the cliff, the building being protected from the waves by a strong
sea-wall of concrete and Portland stone. The building was definitely
opened in August, 1873, while the meeting of the British Association was
being held in the town. Its length is no less than 715 ft., and its
average width 100 ft. The predominant element in the architectural style
of the building is Italian. The following particulars as to the
arrangement and dimensions of the various parts of the building are
derived from the official guide-book:
Entering the gates at the western end, the visitor finds himself at the
top of a flight of granite steps leading to the entrance court, 60 ft.
by 40 ft. The front elevation of the building is 18 ft. high, and
consists of five arches, with terra-cotta columns and enrichments. On
the frieze running round the sides are the appropriate words, “And God
said, Let the waters bring forth abundantly the moving creature that
hath life.” On the northern side of the entrance court is the
restaurant; and on the southern side a series of niches ornamented with
vases. From this outer court, the entrance hall, which is 80 ft. by 45
ft., is approached through three doors. This is furnished with
reading-tables and supplied regularly with periodicals, journals, and
telegrams; while between the pillars supporting the roof are handsome
pedestals, surmounted with large glass vases containing the smaller
interesting marine and fresh-water animals, which would be lost to view
in the larger tanks. In one of the recesses facing the entrance are four
microscopes, in which specimens illustrative of subjects in natural
history connected with the aquarium are constantly exhibited. To the
north of the hall lie the general manager’s offices, the retiring-rooms,
kitchen, &c.; and eastwards, in a direct line with the restaurant, is
the entrance to the western corridor of the aquarium proper. This
corridor, which contains a great many tanks, is the longest of any: it
extends 220 ft., and is broken by a central vestibule, 55 ft. by 45 ft.
The roof, which is groined, is constructed of variegated bricks, and
rests upon columns of Bath stone, polished serpentine marble, and
Aberdeen granite, the carved capitals of the columns having appropriate
marine subjects. On each side are placed the first two series of tanks,
twenty-one in number. These increase in dimensions from 11 ft. by 10 ft.
upwards, the largest measuring over 100 ft. in length by 40 ft. in
width, and holding 110,000 gallons of sea-water. This colossal tank is
the largest in the building, and is devoted to the exhibition of
porpoises, turtles, and other animals of large size. The next largest
tank, 50 ft. by 30 ft., is immediately opposite.
[Illustration:
FIG. 324.—_Sea-Horses_ (_Hippocampus brevirostris_).
]
The eastern end of the western corridor opens upon the conservatory,
which serves as an approach to the rockwork, fernery, and picturesque
cascade, and also to the eastern corridor. Some artificial rockwork,
skirting the north side of the conservatory, is traversed by a stream of
water, broken up at intervals so as to form numerous little bays and
ponds, and utilized for the reception of seals and the larger reptilia.
In the side-space between the conservatory and the second or eastern
corridor are six octagonal table-tanks, of elegant design, for the
exhibition of some of the smaller and more rare marine animals, and, at
the eastern extremity, apparatus which serves to illustrate the hatching
and development of trout and salmon. The entire length of this second
corridor is about 160 ft., one side of the eastern portion, which is 90
ft. by 23 ft., being devoted to the exhibition of fresh-water animals.
At the end of the corridor are situated the curator’s offices and the
naturalists’ room, fitted with open tanks and all necessary appliances;
and the engines, pumps, &c., for supplying the water, and keeping it
constantly aërated.
The system adopted for aërating the water at the Brighton Aquarium is
quite different from that used at the Crystal Palace. In the former the
water is pumped directly from the sea into reservoirs formed under the
floors, and capable of holding 500,000 gallons, which can be filled in
ten hours. From these the water is pumped up into the tanks as required;
but there is no general circulation through the system of tanks and
reservoirs. Each tank is treated independently, and its water is aërated
and kept moving by the injection of air at the lower part, effected by
steam power.
The popularity of the Brighton Aquarium may be judged of from the fact
that the average daily number of visitors is about 9,000, and that on
some occasions nearly twice that number pass the turnstiles. Among the
specialities of the establishment are herring and mackerel, which it has
hitherto been considered impossible to preserve in confinement for any
length of time. They are now thriving well in the Aquarium, although
these fishes are both extremely impatient of confinement. The herring
feed readily upon small shrimps, in catching which they display a
wonderful activity. Fig. 324 shows the curious fish called the
“sea-horse” (_Hippocampus_), from the singular resemblance of the front
part of the body to a horse’s head, or, at least, to that form which
conventionally represents the “knight” among a set of chessmen. The tail
of the creature is prehensile, and enables it to cling to sea-weeds and
other bodies. The sea-horses have thriven well in the Brighton Aquarium,
and also in that at the Crystal Palace. The latest novelties are the
_Proteus_ from the dark caves of Adelsburg, axolotls from Mexico, the
mud-fish (_Lepidosiren annectans_) from the Gambia, and the
telescope-fish from Shanghai. Some of these creatures are of great
interest from the circumstance of their forming the connecting-links
between fishes and reptiles.
[Illustration:
FIG. 325.—_Proteus anguinus._
]