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 KEY TO THE BRANCHES, OR SUB-KINGDOMS

A_{1} One-celled Animals (Protozoans)	I.

A_{2} Many-celled Animals (Metazoans)

B_{1} (around a center). Without head; all aquatic, resembling plants, and often fixed to bottom

C_{1} Walls of body serving as digestive organs

D_{1} Many openings, no tentacles         II. (Porifera)

D_{2} One opening, which is both         III. mouth and vent; tentacles for               (Cœlenterata) seizing prey

C_{2} Digestive tube distinct from body       IV. wall, spiny skin

B_{2} With anterior and posterior end; dorsal and ventral surface

C_{1} Body of successive segments; legs        V.           without joints

C_{2} External skeleton of successive         VI. rings; jointed legs

C_{3} Body soft; no skeleton; usually        VII. bearing a limy shell

C_{4} Internal jointed skeleton, attached   VIII. to 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).

(Which branch? Why?)