Fig. 8—Amœba, showing the forms assumed by a single individual in four successive changes. (From Kellogg's Elementary Zoöl.)
Fig. 9—Euglina virdis. (After Saville Kent.)
Fig. 10—Spirocheta duttoni, × 4500. (After Breinl and Carter.)
The next class which may be known as the whip-bearers (Mastigophora) includes those Protozoa that move by fine undulating processes called flagella. One of the common representatives of this class is the little green Euglena ([Fig. 9]), whose presence in standing ponds and puddles often imparts a greenish color to the water. Then in the salt water near the surface there are often myriads of minute Noctiluca whose wonderfully phosphorescent little bodies glow like coals of fire when the water is disturbed at night. Although this class contains fewer forms than the preceding some of these have within recent years been found to be of great importance because they live as parasites on man and other animals. The trypanosome whose presence in the blood and tissues of the patient causes that dreadful disease which ends in sleeping sickness belongs here as well as do several other similar kinds that produce serious troubles for various mammals and birds. The Spirochæta, about which there has been so much recent discussion, also belong here. These are simple spiral-like forms ([Fig. 10]), that are sometimes classed with the simple plants, bacteria, but Nuttall and others have shown very definitely that they should be classed with the simplest animals, the Protozoans. These are the cause of relapsing fevers in man and of several diseases of domestic animals. It is believed by certain eminent zoölogists that when the germ that causes yellow fever is discovered it will be found to belong to this group.