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 

 Drilophagus 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 quadricomus 

 (enlarged 300 times). 



