The class _Turbellaria_ contains a variety of other worms of a lowly kind, one or two of which (_e.g._, _Borlesia_) live coiled up in complex tangles which, if unravelled, would attain a length of forty feet. Amongst the commoner kinds may be mentioned the worm _Nemertes_, and all worms called _Planariæ_ (which are mostly fresh-water, though some live on land), allied 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.