FIG. 244.--LUNG FISH of Australia (_Ceratodus miolepis_). FIG. 245.--TRUNK FISH. FIG. 246.--SEAWEED FISH. × ¹⁄₅ (_Phyllopteryx eques_). =Remarkable Fish.= SPECIAL REPORTS. (Encyclopedia, texts, dictionary.)] KEY TO THE BRANCHES, OR SUB-KINGDOMS A₁ =One-celled Animals= (_Protozoans_) I. PROTOZOANS A₂ =Many-celled Animals= (_Metazoans_) B₁ RADIATE (around a center). Without head; all aquatic, resembling plants, and often fixed to bottom C₁ Walls of body serving as digestive organs D₁ Many openings, no tentacles II. SPONGES (_Porifera_) D₂ One opening, which is both mouth and III. POLYPS vent; tentacles for seizing prey (_Cœlenterata_) C₂ Digestive tube distinct from body wall, IV. ECHINODERMS spiny skin B₂ BILATERAL. With anterior and posterior end; dorsal and ventral surface C₁ Body of successive segments; legs V. VERMES without joints C₂ External skeleton of successive rings; VI. ARTHROPODS jointed legs C₃ Body soft; no skeleton; usually bearing VII. MOLLUSKS a limy shell C₄ Internal jointed skeleton, attached to VIII. VERTEBRATES an axis or vertebral column =Examples.=--Tell the branch to which each of the following animals belongs: crayfish, earthworm, thousand leg, white grub, sea anemone, ameba, tapeworm, caterpillar, beetle, sparrow, snake, oyster, starfish, fish. Be prepared to state the reason for each classification. The =classes= in the branch =vertebrata= are: 1. Fishes (_pisces_). 2. Frogs and Salamanders (_batrachia_). 3. Reptiles (_reptilia_). 4. Birds (_aves_). 5. Mammals (_mammalia_). [Illustration: FIG. 247.--A SNAIL. (Which branch? Why?)] CHAPTER XI BATRACHIA The theory of evolution teaches that animal life began in a very simple form in the sea, and that afterward the higher sea animals lost their gills and developed lungs and legs and came out to live upon the land; truly a marvelous procedure, and incredible to many, although the process is repeated every spring in countless instances in pond and brook.