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with hammer and chisel； at the expense of much dirt and patience；
for the moment it is touched it contracts deep into the rock； and
all that is left of the daisy flower； some two or three inches
across； is a blue knot of half the size of a marble。 But it will
expand again； after a day or two of captivity； and will repay all
the trouble which it has cost。 Troglodytes may be found； as I have
said already； in hundreds at Hastings； in similar situations to
that of Bellis； its only token； when the tide is down； being a
round dimple in the muddy sand which firs the lower cracks of
rocks。
But you will want more than these anemones； both for your own
amusement； and for the health of your tank。 Microscopic animals
will breed； and will also die； and you need for them some such
scavenger as our poor friend Squinado； to whom you were introduced
a few pages back。 Turn； then； a few stones which lie piled on each
other at extreme low…water mark； and five minutes' search will give
you the very animal you want； … a little crab； of a dingy russet
above； and on the under side like smooth porcelain。 His back is
quite flat； and so are his large angular fringed claws； which； when
he folds them up； lie in the same plane with his shell； and fit
neatly into its edges。 Compact little rogue that he is； made
especially for sidling in and out of cracks and crannies； he
carries with him such an apparatus of combs and brushes as Isidor
or Floris never dreamed of； with which he sweeps out of the sea…
water at every moment shoals of minute animalcules； and sucks them
into his tiny mouth。 Mr。 Gosse will tell you more of this marvel；
in his 〃Aquarium；〃 p。 48。
Next； your sea…weeds； if they thrive as they ought to do； will sow
their minute spores in millions around them； and these； as they
vegetate； will form a green film on the inside of the glass；
spoiling your prospect： you may rub it off for yourself； if you
will； with a rag fastened to a stick； but if you wish at once to
save yourself trouble； and to see how all emergencies in nature are
provided for； you will set three or four live shells to do it for
you； and to keep your sub…aqueous lawn close mown。
That last word is no figure of speech。 Look among the beds of sea…
weed for a few of the bright yellow or green sea…snails （Nerita）；
or Conical Tops （Trochus）； especially that beautiful pink one
spotted with brown （Ziziphinus）； which you are sure to find about
shaded rock…ledges at dead low tide； and put them into your
aquarium。 For the present； they will only nibble the green ulvae；
but when the film of young weed begins to form； you will see it
mown off every morning as fast as it grows； in little semicircular
sweeps； just as if a fairy's scythe had been at work during the
night。
And a scythe has been at work； none other than the tongue of the
little shell…fish； a description of its extraordinary mechanism
（too long to quote here； but which is well worth reading） may be
found in Gosse's 〃Aquarium。〃 （32）
A prawn or two； and a few minute star…fish； will make your aquarium
complete； though you may add to it endlessly； as one glance at the
salt…water tanks of the Zoological Gardens； and the strange and
beautiful forms which they contain； will prove to you sufficiently。
You have two more enemies to guard against； dust； and heat。 If the
surface of the water becomes clogged with dust； the communication
between it and the life…giving oxygen of the air is cut off； and
then your animals are liable to die； for the very same reason that
fish die in a pond which is long frozen over； unless a hole be
broken in the ice to admit the air。 You must guard against this by
occasional stirring of the surface； or； as I have already said； by
syringing and by keeping on a cover。 A piece of muslin tied over
will do； but a better defence is a plate of glass； raised on wire
some half…inch above the edge； so as to admit the air。 I am not
sure that a sheet of brown paper laid over the vase is not the best
of all； because that； by its shade； also guards against the next
evil； which is heat。 Against that you must guard by putting a
curtain of muslin or oiled paper between the vase and the sun； if
it be very fierce； or simply （for simple expedients are best） by
laying a handkerchief over it till the heat is past。 But if you
leave your vase in a sunny window long enough to let the water get
tepid； all is over with your pets。 Half an hour's boiling may
frustrate the care of weeks。 And yet； on the other hand； light you
must have； and you can hardly have too much。 Some animals
certainly prefer shade； and hide in the darkest crannies； and for
them； if your aquarium is large enough； you must provide shade； by
arranging the bits of stone into piles and caverns。 But without
light； your sea…weeds will neither thrive nor keep the water sweet。
With plenty of light you will see； to quote Mr。 Gosse once more；
（33） 〃thousands of tiny globules forming on every plant； and even
all over the stones； where the infant vegetation is beginning to
grow； and these globules presently rise in rapid succession to the
surface all over the vessel； and this process goes on
uninterruptedly as long as the rays of the sun are uninterrupted。
〃Now these globules consist of PURE OXYGEN； given out by the plants
under the stimulus of light； and to this oxygen the animals in the
tank owe their life。 The difference between the profusion of
oxygen…bubbles produced on a sunny day； and the paucity of those
seen on a dark cloudy day； or in a northern aspect； is very
marked。〃 Choose； therefore； a south or east window； but draw down
the blind； or throw a handkerchief over all if the heat become
fierce。 The water should always feel cold to your hand； let the
temperature outside be what it may。
Next； you must make up for evaporation by FRESH water （a very
little will suffice）； as often as in summer you find the water in
your vase sink below its original level； and prevent the water from
getting too salt。 For the salts； remember； do not evaporate with
the water； and if you left the vase in the sun for a few weeks； it
would become a mere brine…pan。
But how will you move your treasures up to town？
The simplest plan which I have found successful is an earthen jar。
You may buy them with a cover which screws on with two iron clasps。
If you do not find such； a piece of oilskin tied over the mouth is
enough。 But do not fill the jar full of water； leave about a
quarter of the contents in empty air； which the water may absorb；
and so keep itself fresh。 And any pieces of stone； or oysters；
which you send up； hang by a string from the mouth； that they may
not hurt tender animals by rolling about the bottom。 With these
simple precautions； anything which you are likely to find will well
endure forty…eight hours of travel。
What if the water fails； after all？
Then Mr。 Gosse's artificial sea…water will form a perfect
substitute。 You may buy the requisite salts （for there are more
salts than 〃salt〃 in sea…water） from any chemist to whom Mr。 Gosse
has entrusted his discovery； and； according to his directions； make
sea…water for yourself
One more hint before we part。 If； after all； you are not going
down to the sea…side this year； and have no opportunities of
testing 〃the wonders of the shore；〃 you may still study Natural
History in your own drawing…room； by looking a little into 〃the
wonders of the pond。〃
I am not jesting； a fresh…water aquarium； though by no means as
beautiful as a salt…water one； is even more easily established。 A
glass jar； floored with two or three inches of pond…mud （which
should be covered with fine gravel to prevent the mud washing up）；
a specimen of each of two water…plants which you may buy now at any
good shop in Covent Garden； Vallisneria spiralis （which is said to
give to the Canvas…backed duck of America its peculiar richness of
flavour）； and Anacharis alsinastrum； that magical weed which；
lately introduced from Canada among timber； has multiplied； self…
sown； to so prodigious an extent； that it bid fair； a few years
since； to choke the navigation not only of our canals and fen…
rivers； but of the Thames itself： （34） or； in default of these；
some of the more delicate pond…weeds； such as Callitriche；
Potamogeton pusillum； and； best of all； perhaps； the beautiful
Water…Milfoil （Myriophyllium）； whose comb…like leaves are the
haunts of numberless rare and curious animalcules：… these （in
themselves； from the transparency of their circulation； interesting
microscopic objects） for oxygen…breeding vegetables； and for
animals； the pickings of any pond； a minnow or two； an eft； a few
of the delicate pond…snails （unless they devour your plants too
rapidly）： water…beetles； of a