This discarded skin still has working eye lenses. You could look right through them.

 

When a jumping spider molts, it doesn't just shed its exoskeleton, it leaves behind a nearly perfect glass copy of its own eyes. The corneal lenses in the empty eye sockets stay completely clear and transparent, because the shed skin is made of only the outer layer of cuticle, without any of the tissue that usually makes a living spider opaque.

Scientists have measured just how clear these lenses really are. The corneas of jumping spider eyes let through almost 100 percent of the light in the spider's visible range, and researchers examining shed skins under a microscope confirmed the eye lenses stayed fully transparent even after the spider had moved on.

Here is the catch. What is left behind is only the lens, a small clear window with nothing behind it. The retina, the photoreceptors, and the nerves that actually turn light into an image left with the living spider. So while you genuinely can hold up an empty eye lens and see light pass straight through it, the shed skin itself cannot see anything. It is a leftover window, not a leftover eye.

Jumping spiders molt several times over their lives as they grow, and each cast off skin, called an exuvia, is a strange little time capsule. Every hair, every joint, and every lens is preserved in miniature, clear enough that you could look through the eyes of a creature that has already outgrown them.