CHAPTER X
FISHES
Suggestions.—The behavior of a live fish in clear water, preferably in a glass vessel or an aquarium, should be studied. A skeleton may be prepared by placing a fish in the reach of ants. Skeletons of animals placed on ant beds are cleaned very thoroughly. The study of the perch, that follows, will apply to almost any common fish.
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Movements and External Features.—What is the general shape of the body of a fish? How does the dorsal, or
upper, region differ in form from the ventral? Is there a
narrow part or neck where the head joins the trunk?
Where is the body thickest? What is the ratio between
the length and height? (Fig. 209.) Are the right and left
sides alike? Is the symmetry of the fish bilateral or
radial?
The body of the fish may be divided into three regions,—the head, trunk, and tail. The trunk begins with the foremost scales; the tail is said to begin at the vent, or anus. Which regions bear appendages? Is the head movable independently of the trunk, or do they move together? State the advantage or disadvantage in this. Is the body depressed (flattened vertically) or compressed
