Environmental oxygen triggers loss of webbed digits

Free fingers have many obvious advantages on land, such as in locomotion and grasping, while webbed fingers are typical of aquatic or gliding animals. But both amphibians and amniotes—which include mammals, reptiles, and ...

Embryo

An embryo (irregularly from Greek: ἔμβρυον, plural ἔμβρυα, lit. "that which grows," from en- "in" + bryein "to swell, be full"; the proper Latinate form would be embryum) is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination. In humans, it is called an embryo until about eight weeks after fertilization (i.e. ten weeks LMP), and from then it is instead called a fetus.

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