ESL / EFL Quiz 264

This dreamy illustration of a zebrafish embryo happens to be attached to some cool research. The compilation photo reflects a centuries old observationthat during a certain point in a vertebrate embryos development, the embryo will look just like embryos of other vertebrates. The concept is known as the developmental hourglass. Embryos look alike in the middle of development, but early and late in development, the embryos appearances diverge, just as an hourglass flares out from its narrow waist.