lied to the flukes.

The class of tape-worms (_Cestoidea_) is one most numerous in its kinds,
which are all completely parasitic in habit. Some of them are so fatal
in their effects that they are estimated to occasion every seventh death
which occurs in Iceland, and they cause mortality amidst our own flocks,
producing in sheep the disease known as the "staggers."

Certain minute organisms, familiarly known as "Wheel-Animalcules," or
Rotifers, form the "class" _Rotifera_. They have gained their name
through an apparently (though, of course, not really) rotary motion, of
that end of their bodies at which the mouth is situated. Here also may
be mentioned certain curious aquatic worms called _Gasterotricha_, which
are closely allied to the wheel animalcules.

Finally may be mentioned the class _Gephyrea_, containing animals,
worm-like indeed in form, but which have much apparent affinity to the
group next to be spoken of--the group of star-fishes and their allies.
Amongst the _Gephyrea_ may be mentioned the worms called _Sipunculus_
and _Priapulus_.

This leads us to the sub-kingdom containing the star-fishes--the
sub-kingdom ECHINODERMA, which includes, besides the star-fishes (or
_Asteridea_), all sea-eggs or sea-urchins (_Echinidea_), the
brittle-stars _Ophiuridea_, as well as the elongated soft animals called
sea-cucumbers, or _Holothuridea_, some of which latter are known as the
Japanese edible, "Trepang."

Besides these groups there are still surviving a few creatures
(_Comatula_ and _Pentacrinus_) belonging to the class of "sea-lilies,"
or _Crinoidea_, creatures which once lived in countless multitudes, but
have now almost entirely passed away. All these crinoids were like
star-fishes on stalks, and of the existing forms, _Pentacrinus_ still
passes the whole of its life, and _Comatula_ its youth, in a stalked
condition.

The next great primary division, or sub-kingdom of animals, is
COELENTERA, and a good type of the coelenterates, the sea anemone
(_Actinia_), has now become a familiar object to us in our aquaria.
These animals are plant-animals, or zoophytes, and some of them build up
coral-reefs, or islands, and it is one kind which produces the red coral
of commerce. Forms essentially similar, but the solid supporting
framework of which is of a softer nature, are such as _Alcyonium_ and
_Pennatula_. All these belong to the "class" _Actinozoa_. There are
other coelenterates of an active free-swimming habit,