the fish immovable, slightly movable, or freely movable? Can it look with both eyes at the same object? Is the range of vision more upward or downward? To the front or side? In what direction is vision impossible? Can a fish close its eyes in sleep? Does the eyeball appear spherical or flattened in front? The ball is really spherical, the lens is very convex, and fish are nearsighted. Far sight would be useless in a dense medium like water.
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Fig. 210.—Blackboard Outline of Fish.
In what direction are the nostrils from the eyes? (Fig. 211.) There are two pairs of nostrils, but only one pair of nasal cavities, with two nostrils opening into each. There are no nasal passages to the mouth, as the test with a probe shows that the cavities do not open into the mouth. What two functions has the nose in man? What function has it in the fish?
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Fig. 211.—Head of Carp.
There are no external ears. The ear sacs are embedded in the bones of the skull. Is hearing acute or dull? When fishing, is it more necessary not to talk or to step lightly, so as not to jar the boat or bank?
What is the use of the large openings found at the back of the head on each side? (Fig. 211.) Under the skin at the sides of the head are thin membrane bones formed from the skin; they aid the skin in protection. Just under these membrane bones are the gill covers, of true bone. Which
