ow I think of it," continued Jack, "it seems to me that the surest
way of arranging your tank so as to get it to keep pure and in good
condition, will be to imitate the ocean in it. In fact make it a
miniature Pacific. I don't see how you can hope to succeed unless you do
that."

"Most true," said I, pondering what my companion said. "But I fear that
that will be very difficult."

"Not at all," cried Jack, rolling his towel up into a ball, and throwing
it into the face of Peterkin, who had been grinning and winking at him
during the last five minutes. "Not at all. Look here. There is water
of a certain saltness in the sea; well, fill your tank with sea water,
and keep it at that saltness by marking the height at which the water
stands on the sides. When it evaporates a little, pour in _fresh_ water
from the brook till it comes up to the mark, and then it will be right,
for the salt does not evaporate with the water. Then, there's lots of
sea-weed in the sea;--well, go and get one or two bits of sea-weed, and
put them into your tank. Of course the weed must be alive, and growing
to little stones; or you can chip a bit off the rocks with the weed
sticking to it. Then, if you like, you can throw a little sand and
gravel into your tank, and the thing's complete."

"Nay, not quite," said Peterkin, who had been gravely attentive to this
off-hand advice, "not quite; you must first make three little men to dive
in it before it can be said to be perfect, and that would be rather
difficult, I fear, for two of them would require to be philosophers. But
hallo! what's this? I say, Ralph, look here. There's one o' your crabs
up to something uncommon. It's performing the most remarkable operation
for a crab I ever saw,--taking off its coat, I do believe, before going
to bed!"

We hastily stooped over the tank, and certainly were not a little amused
at the conduct of one of the crabs which still survived it companions. It
was one of the common small crabs, like to those that are found running
about everywhere on the coasts of England. While we gazed at it, we
observed its back to split away from the lower part of its body, and out
of the gap thus formed came a soft lump which moved and writhed
unceasingly. This lump continued to increase in size until it appeared
like a bunch of crab's legs: and, indeed, such it proved in a very few
minutes to be; for the points of the toes were at length extricated from
this hole