IGCSE Biology 4th edition

Biology books by
D G Mackean


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The frog has a loose-fitting moist skin. Its eyes protrude in such a way that they are above water when the rest of the body is immersed. The eyes have movable lids but, in addition, the whole eyeball can be withdrawn farther into the head by muscles. Its nostrils are situated so that air can be breathed while the frog is swimming at the surface; they can also be closed. Behind the eyes are circular ear-drums. Sounds in the air or water set these thin membranes vibrating, the vibration being transmitted by a small bone to a sensory region which sends nervous impulses to the brain.

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