rged with the oxygen necessary to the life of the organisms. It
is not pumped into the tanks directly from the sea, but from three large
cisterns (containing 300 cubic metres), to which it again returns from
the tanks. The water wasted or evaporated during this process is
replaced by new water pumped into the cisterns directly from the sea.
The water flows from the large cisterns into a smaller cistern, from
which it is distributed by means of an electric pump through vulcanite
or lead pipes to the various tanks. The water with which the tanks on
the upper floors are filled is first pumped into large wooden tanks
placed beneath the roof, thence it flows, under almost constant
pressure, into the tanks. The water circulated in this manner contains
by far the largest number of such animals as are capable of living in
captivity in good condition. Some of them even increase at an
undesirable rate, and it sometimes happens that young Mytilus or Ciona
stop up the pipes; in laying these, therefore, due regard must be had to
the arrangements for cleaning. For the cultivation of very delicate
animals it is necessary to keep the water absolutely free from harmful
bacteria; for this purpose large sand-filters have lately been placed in
the system, through which the water passes after leaving the cisterns.
Each of the smaller cisterns, which are fixed in the workrooms, consist
of two water-tanks, placed one above the other; their frames are of
wrought iron and the walls generally of glass. Vessels containing minute
animals can be placed between these two tanks, receiving their water
through a siphon from the upper tank; the water afterwards flows away
into the lower tank.

"The twenty-six tanks of the public aquarium (the largest of which
contains 112 cubic metres of water) have stone walls, the front portion
alone being made of glass. As the tanks hold a very large number of
animals in proportion to the quantity of water, they require to be well
aerated. The pipes through which the water is conducted are therefore
placed above the surface of the water, and the fresh supply is driven
through them under strong pressure. A large quantity of air in the form
of fine bubbles is thus taken to the bottom of the tank and distributed
through the entire mass of water. Should the organisms which it is
desired to keep alive be very minute, there is a danger of their being
washed away by the circulating water. To obviate this, either the water
w