Cephalopod eyes

Cephalopod eyes are no different from human eyes. To say the least, there is not much difference. But the corneas of octopus eyes are not connected together, and there is a wide hole in the center.

However, the adjustment of human eyes, that is, the adjustment of the focal length of objects at different distances, is accomplished by changing the curvature of the lens, while octopus adjusts its vision by moving away from and close to the retina, just like a camera rotates its lens. Octopus eyelids are also different from human eyes when they are closed. Octopus eyelids have annular muscles. When they close their eyes, they cover them like a camera's mirror shutter.

No animal in the ocean has such sensitive eyes as octopus and its relatives. Only the eyes of owls, cats and people can match those of octopus. This is because about 63,000 cone cells per square millimeter receive light on the retina of octopus eyes. Squid and squid have more cones, which are 105000 and 162000 respectively. Spider is16000; There are 50,000 carp; There are 397,000 cats, 400,000 people and 680,000 owls.

Cephalopod mollusks have unusually large eyes. The diameter of squid eyes is smaller than the thickness of its trunk 10 times. The eyes of the king squid are as big as small wheels, and the diameter can reach 40 cm. A 30-meter-long blue whale's eyes are only 10-20 cm. But the most unusual thing is the eyes of deep-water squid: some stand upright like telescopes; Others are born on slender stalks and extend far to both sides; Some eyes are asymmetrical: the left eye is three times larger than the right eye. So, how does this squid with asymmetrical eyes swim? You know, their heads are unbalanced. Probably it takes them a lot of effort to keep their balance, so that they won't roll left and right when swimming forward. Scientists believe that big eyes are the result of adapting to the living environment in the deep sea, and its powerful optical system absorbs the dim light in the deep sea. Squids living by the sea can see everything around them with small eyes.

Squid has very special "eyes" that can sense temperature. You can't find any other animal in nature with such "eyes" that can sense temperature. It turns out that there are about 30 small thermometers on the fins of deep-water squid that can accept heat rays. These thermometers are distributed on the skin in the form of black spots. Under the microscope, it is composed of a spherical capsule filled with transparent substances, and the surface of the capsule is covered with a thick layer of red blood cells-a filter, only infrared rays can pass through, and other light rays are blocked.

There seems to be a photon chemical process in the temperature-sensitive "eyes" of squid, just like what happens in the retina or photographic film of ordinary eyes. The energy absorbed by this organ leads to the recombination of photosensitive molecules (squid is a temperature-sensitive molecule). After these photosensitive molecules act on the nerves, they form images of the objects they see in the brain.

American rattlesnakes and armored snakes living in Siberia also have special thermometers, but they are thermocouples with different structures. With the help of a thermometer, snakes look for warm-blooded animals such as rodents and birds in the dark. Like all heating bodies, these animals emit infrared rays.

What is the use of squid's "temperature eye"? In the depths of the ocean where they live, there is no such warm-blooded animal! Really not? No, greedy sperm whales prey on squid in the depths of the ocean. A sperm whale can eat tons of squid every day, and 95% of the diet of these big whales is deep-water squid. It can be seen that this is why squid need to "see" the temperature in the depths of the cold sea. Although there are no warm-blooded animals there, there will be greedy behemoths fleeing from the crystal clear sea to this dark kingdom. The thermometer warned the squid that a strong enemy was coming.