Bats are tetrapods, or four-legged animals. They have two pairs of limbs, like mammals, birds, reptiles, and amphibians, even though their forelimbs are wings and their hindlimbs are used for hanging upside down when they are not flying. Like all tetrapods, they share a fundamental limb pattern of “one bone, two bones, lots of bones, and digits.” In this image of a fruit bat (Carollia perspicillata) embryo stained to reveal bones (red) and cartilage (blue), one of the forelimbs can be seen running from left to right, ending with five elongated digits. These will become part of the adult bat’s wing. Other notable features include the lattice-like pattern of the developing skull, the eye, the vertebral column, and the ribcage.
Scott Weatherbee PhD, Dept. Genetics, Yale University School of Medicine
The embryo was fixed at a specific time during development—specifically, developmental stage 17. It was then stained with Alcian Blue to highlight all of the cartilage and with Alizarin Red to highlight the bone in the embryo. Following staining it was treated with chemicals to remove all the soft tissue and photographed with a light microscope.