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The occurrence of an internal skeleton, in definite relations to the other organ systems, and the articulation of the body into homologous segments, are points in the general organization of Vertebrates to which especial weight must be given. This metameric structure is more or less definitely expressed in most of the…
In fact, contrary to all of the early anecdotes claiming that practice has no effect on the onset of walking, one carefully controlled study has shown that special exercise can indeed accelerate it. In this study, a group of newborns were given just ten minutes per day of "practice walking." Every day between one and…
An early classic experiment by the Nobel Prize-winning embryologist Roger Sperry illustrates the principle perfectly. Sperry and a colleague took a tadpole and removed a tiny square of skin from the back. They removed another square, the same size, from the belly. They then regrafted the two squares, but each in the…