十万个为什么·科学阅读30篇（2）

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为什么某些深海鱼拥有透明的头部？

The barreleye fish lives 600–800 meters deep where sunlight barely penetrates the ocean surface.
Its dome-shaped, transparent head shields two upward-facing tubular eyes packed with light-sensitive rods.
This clear casing protects delicate retinas while allowing maximum photon capture in near-total darkness.
Inside the dome, fluid-filled tissue maintains optical clarity and internal pressure balance.
The fish rotates its eyes independently—to scan overhead for bioluminescent prey or predators above.
Its brain lies directly beneath the dome, surrounded by a gelatinous matrix that transmits light without distortion.
Unlike opaque skulls, transparency eliminates internal shadows that would blur vision in dim environments.
CT scans reveal bony struts reinforcing the dome without obstructing visual fields.
Evolution favored this design because detecting faint glows is more critical than camouflage at such depths.
Biologists study its optics to improve low-light imaging sensors for underwater exploration.