Blind Cave Form
A. mexicanus is famous for its blind cave form, which is known by such names as blind cave tetra, blind tetra, and blind cavefish. Some thirty distinct populations of Mexican tetras live in deep caves and have lost the power of sight and even their eyes. These fish can still, however, find their way around by means of their lateral lines, which are highly sensitive to fluctuating water pressure.
The eyed and eyeless forms of A. mexicanus, being members of the same species, are closely related and can interbreed. Astyanax jordani, however, is another blind cave fish, independently and recently evolved from the sighted surface form, which is sometimes confused with the cave form of A. mexicanus. However, when born, the cave dwelling form of A. mexicanus has eyes. As they grow older, skin just grows over them and the eyes degenerate completely, because there is no need for sight in the pitch-black world of a cave.
Read more about this topic: Mexican Tetra
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—Herman Melville (1819–1891)
“Do you know how poetry started? I always think that it started when a cave boy came running back to the cave, through the tall grass, shouting as he ran, “Wolf, wolf,” and there was no wolf. His baboon-like parents, great sticklers for the truth, gave him a hiding, no doubt, but poetry had been born—the tall story had been born in the tall grass.”
—Vladimir Nabokov (1899–1977)
“Once out of nature I shall never take
My bodily form from any natural thing,
But such a form as Grecian goldsmiths make”
—William Butler Yeats (1865–1939)