If time and circumstances allow a prolonged study, several additional facts may be observed by the pupil, _e.g._ Does the paramecium swim with the same end always foremost, and same side uppermost? Can it move backwards? Avoid obstacles? Change shape in a narrow passage? Does refuse matter leave the body at any particular place? Trace movement of the food particles. Draw the paramecium. Which has more permanent parts, the _ameba_ or _paramecium_? Name two anatomical similarities and three differences; four functional similarities and three differences. The ameba belongs in the class of protozoans called _Rhizopoda_ “root footed.” =Other classes of Protozoans= are the _Infusorians_, which have many waving cilia (Fig. 17) or one whip-like flagellum (Fig. 18), and the _Foraminifers_ which possess a calcareous shell pierced with holes. Much chalky limestone has been formed of their shells. These and the radiolarians, which have flinty shells (Fig. 19), are often placed in the class rhizopoda. To which class does the paramecium belong? Protozoans furnish a large amount of food to the higher animals. =To the Teacher.= If plant, animal, and human biology are to be given in one year as planned, and full time allowed for practical work, the portions of the text in small type, as Chapter III, may be omitted or merely read and discussed. Any two of the three parts forming the course may be used for a year’s course by using all of the text and spending more time on practical and field work. CHAPTER III SPONGES SUGGESTIONS.--In many parts of the United States, fresh-water sponges may, by careful searching, be found growing on rocks and logs in clear water. They are brown, creamy, or greenish in color, and resemble more a cushion-like plant than an animal. They have a characteristic gritty feel. They soon die after removal to an aquarium. A number of common small bath sponges may be bought and kept for use in studying the skeleton of an ocean sponge. These sponges should not have large holes in the bottom; if so, too much of the sponge has been cut away. A piece of marine sponge preserved in alcohol or formalin may be used for showing the sponge with its flesh in place. Microscopic slides may be used for showing the spicules. [Illustration: FIG. 21.--FRESH-WATER SPONGE.] [Illustration: FIG. 22.--SECTION of fresh-water sponge (enlarged).] The small =fresh-water sponge= (Fig. 21) lacks the more or less vase-like form typical of sponges. It is a rounded mass growing upon a rock or log. As indicated by the arrows, where does _water enter_ the sponge? This may be tested by putting coloring matter in the water near the living sponge. Where does the _water come out_? (Fig. 22.) Does it pass through _ciliated chambers_ in its course? Is the _surface_ of the sponge rough or smooth? Do any of the skeletal _spicules_ show on the surface? (Fig. 21.) Does the sponge thin out near its edge?