6
THE ESSEX NATURALIST.
tissue, and pass to the surface cells along definite tracks. No
doubt the rhabdites give a considerable amount of support to
the body and yet permit freedom of movement. They are
analogous to an external skeleton, made up of small parts, which
articulate freely—a variety of chain armour. Then, too, the
rhabdites can be discharged, and on coming into contact with
water, produce a slimy substance. In addition to this, planarians
have special glands developed on the lateral margins, which
produce mucus. This mucus serves as a protection and is used
in the capture of prey. Sometimes threads of it are formed and
are used by the animal to lower itself through the water. (See
p. 2.)
COLLECTION AND PRESERVATION. Planarians
should be searched for in fresh water, under stones and on the
shaded parts of submerged plants. Planaria alpina may be
found in cold springs and mountain streams. Flowing streams,
rivers, lakes and ponds are all suitable hunting grounds.
Bdellocephala punctata lives in mud, which it leaves only for the
purpose of depositing cocoons. Bohmig (3) suggests wrapping
up bait, such as a dead frog, in gauze and leaving it in a pond
or stream for a few days.
When collecting planarians, care should be taken that no
animals likely to die and set up decomposition remain in the
tube containing them. The water must be prevented from
becoming warm during transportation, as planarians soon die
and disintegrate under sudden changes of temperature.
Identification of species should be made, when possible, on
living animals; it is often difficult to diagnose dead specimens,
especially when they are not sexually mature.
Planarians do not make very satisfactory preparations, as
they always contract, in spite of every care. Steinmann and
Bresslau (36) recommend the following solution for killing:—
Commercial nitric acid, 1 part: a saturated solution of mercuric
chloride in a 5% solution of common salt, 1 part; distilled water,
I part. The animal is placed on a sheet of glass with the smallest
quantity of water possible. As soon as the planarian extends
itself, the solution is poured over it quickly and the creature is
left in the fluid not longer than one minute. It is then placed