Huden Der Ser

Den fjerde morgen var Chiara forsinket. Hun kom ind med to kopper kaffe fra hjørnecaféen. "Vi har ikke lavet farvetesten for Polly," sagde hun.

The fourth morning, Chiara was running late. She came in with two coffees from the corner bar. "We have not done the colour test for Polly," she said.

Hun satte tre tallerkener på bunden af tanken. Klar rød. Klar blå. Klar gul. Under en af dem dækkede en lille kuppel et stykke rejer. I dag var rejen under den røde tallerken.

She put three plates on the tank floor. Bright red. Bright blue. Bright yellow. Under one of them, a small dome covered a piece of shrimp. Today, the shrimp was under the red plate.

"Her er det mærkelige," sagde Chiara. "Blæksprutter er farveblinde. Deres øjne har kun én type fotoreceptor. Ifølge alle tests, vi nogensinde har lavet på deres øjne, kan de ikke skelne farver."

"Here is the strange thing," Chiara said. "Octopuses are colour-blind. Their eyes have only one kind of photoreceptor. By every test we have ever done on their eyes, they cannot tell colours apart."

Polly vippede hovedet.

Polly tilted her head.

"Og alligevel," sagde Chiara. "Se."

"And yet," Chiara said. "Watch."

Pasta rullede sig ud. To arme strakte sig ud over tankens bund. De passerede den blå tallerken uden at sænke farten. De passerede den gule tallerken uden at sænke farten. De stoppede over den røde tallerken. En arm løftede kuplen. Pasta tog rejen.

Pasta uncurled. Two arms went out across the tank floor. They passed over the blue plate without slowing. They passed over the yellow plate without slowing. They paused over the red plate. One arm lifted the dome. Pasta took the shrimp.

"Hun er ikke blind for farver," sagde Chiara. "Men det er ikke hendes øjne, der ser det."

"She is not blind to colour," Chiara said. "But it is not her eyes that see it."

I de sidste femten år har biologer opdaget, at blækspruttehud er fuld af lysfølsomme celler. De samme molekyler, der findes i en menneskelig nethinde, findes på overfladen af en blækspruttearm. Huden kan registrere forskellige lysbølgelængder. I nogle arter kan huden registrere specifikke farver.

In the last fifteen years, biologists have discovered that octopus skin is full of light-sensing cells. The same molecules that line a human retina line the surface of an octopus arm. The skin can detect different wavelengths of light. In some species, the skin can detect specific colours.

Dette er et svar på et gammelt mysterium: hvordan kan et farveblindt dyr kamuflere sig perfekt i farverige omgivelser? En blæksprutte på koral matcher korallen. En blæksprutte på sand matcher sandet. Dens øjne kan ikke se farver. Men dens hud kan. Huden ser, hvad huden skal kopiere.

This is one answer to an old puzzle: how does a colour-blind animal camouflage itself perfectly into colourful environments? An octopus on coral matches the coral. An octopus on sand matches the sand. Its eyes cannot see colour. But its skin can. The skin sees what the skin needs to copy.

Polly gik langsomt langs kanten af tanken. Hun havde aldrig tænkt på sine egne øjne før. Tanken om, at et dyr kunne se med andre dele af sig selv end sine øjne, var mærkelig.

Polly walked along the rim of the tank slowly. She had never thought about her own eyes before. The idea that an animal could see with parts of itself other than its eyes was strange.

"Vi har udgivet artikler om dette i et årti," sagde Chiara. "De fleste mennesker kan stadig ikke tro det. Dyrets hud ser."

"We have published papers on this for a decade," Chiara said. "Most people still cannot believe it. The animal's skin sees."