The photographs feature fish that have been specially treated to make the stained skeletal tissues visible through the skin and flesh. The technique, developed by Dr. Adam Summers, uses dyes, hydrogen peroxide, a digestive enzyme and glycerin to make the flesh seem to disappear. Photo: This image of the butterfly ray (Gymnura crebripunctata) helped scientists study the joints in its wings. (Photo by Adam Summers)

A woman wears a flower crown during a Summer Solstice celebration on June 21, 2021 in Krakow, Poland. The summer solstice represents the longest day of the year, with the most hours of sunlight, and is celebrated by various cultures worldwide. (Photo by Omar Marques/Getty Images)

Nicole Scherzinger at the “The X Factor” TV show, Series 14, Episode 15, Judges' Houses in Sun City, South Africa on October 21, 2017. (Photo by Dymond/Thames/Syco/Rex Features/Shutterstock)

Hundreds of hardy swimmers across Britain braved jumping into freezing cold waters for a annual Christmas Day dip on December 25, 2017. (Photo by Dave Nelson/The Sun)

Sun Rongchun, 57, exercises with an improvised cervical traction device attached to a high bar at a sports complex in Shenyang, Liaoning province, China on April 9, 2019. (Photo by Sheng Li/Reuters)

Dario Sammartino, of Italy, competes at the final table during the World Series of Poker at the Rio hotel-casino in Las Vegas Sunday, July 14, 2019. (Photo by Steve Marcus/Las Vegas Sun via AP Photo)

The sun sets on Walney Island, Cumbria, county in North West England on October 10, 2019. Today will be unsettled with spells of heavy rain. (Photo by GREENBURN/Alamy Live News)

Iceland horses play on a meadow of a stud farm in Obernhain near Frankfurt, Germany, as the sun rises Thursday, July 23, 2020. (Photo by Michael Probst/AP Photo)