Bats

Cuvier uses the metaphor of impressions for the way that a bat flies through the air. He believes that bats fly through the air in the dark by recieiving signals on their skin. He uses impressions to describe this because he makes a reference to the printing press. He wrote the paragraph in 1827, so he wouldn't have known about radar or sonar...he would have known about the printing press.

He feels that bats get signals on their skin, similar to the way that words are imprinted on paper by the printing press. The technology wasn't around in the early 1800s to know that bats really maneuvered around obstacles in the dark by sending out high-frequency sounds and then getting them back after they bounce off an obstacle. At the time, impression was the best metaphor to describe the way that scientists thought bats flew in the dark.