KEY TO THE BRANCHES, OR SUB-KINGDOMS
A_{1} One-celled Animals (Protozoans) I. Protozoans
A_{2} Many-celled Animals (Metazoans)
B_{1} Radiate (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. Sponges
(Porifera)
D_{2} One opening, which is both III. Polyps
mouth and vent; tentacles for (Cœlenterata)
seizing prey
C_{2} Digestive tube distinct from body IV. Echinoderms
wall, spiny skin
B_{2} Bilateral. With anterior and posterior
end; dorsal and ventral surface
C_{1} Body of successive segments; legs V. Vermes
without joints
C_{2} External skeleton of successive VI. Arthropods
rings; jointed legs
C_{3} Body soft; no skeleton; usually VII. Mollusks
bearing a limy shell
C_{4} Internal jointed skeleton, attached VIII. Vertebrates
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).
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Fig. 247.—A Snail. (Which branch? Why?)
