446 
WORMS. 
animalcules are divisible into four orders. Of these, the Ploima may be considered 
the typical order of the class, on account of the numbers of genera, the abundance 
of species, and the restless energy, perfection of structure, and superior intelligence 
of its members. Locomotion is effected by means of swimming with the ciliary 
wreath. The order is divided into two sections, the Loricata, which, as in Noteus, 
represented in the annexed illustra¬ 
tion, are protected by an enclosing 
shell, and the Illoricata, which, as 
exemplified by Notommata, have the 
integument flexible, and the body not 
protected in a shelly case. The 
habits of the group show considerable 
variation. Many species may be found 
swimming freely or attached to water- 
weeds in almost any pond, stream, or 
stagnant ditch; and others, like 
Brachionus, one of the Loricata, may 
be seen riding in clusters on the backs 
and sides of crustaceans. Amongst the 
Illoricata, Balatro calvus — remark¬ 
able for having no disc—infests small 
water-worms, to which it clings by 
its enlarged foot - processes; and 
Brilophagus bucephalus is parasitic 
upon a water - worm ( Lumbriculus ), 
to which it clings, feeding by means 
of its modified jaws. Other species 
again form internal parasites, the 
genus Albertia being found in the 
interior of earth-worms, slugs, and 
annelids of the genus Nais ; while 
Notommata may be seen swimming 
freely within the spheres of the 
beautiful Volvox. 
The members of the order Bdel- 
loidea swim by means of their ciliary 
wreath, and creep about like a leech. 
The foot is telescopically retractile, and ends almost invariably in three toes or 
claspers. In this group also the mode of life is varied. Most species are free- 
living, but others attach themselves to various entomostracous crustaceans, and 
Callidina parasitica is always found clinging to the appendages of the fresh¬ 
water shrimp and the aquatic wood-louse. A special interest attaches to this 
group on account of their vitality. If specimens be enclosed in a cell containing 
a little sand or moss, the contents may be dried over sulphuric acid or heated 
up to 200° F., or left to the neglected dust of years, and some of the little creatures 
will revive if a drop or two of fresh water be added to the sand. 
FOUR-HORNED ROTIFER, Noteus qUCUlricOmUS 
(enlarged 300 times). 
