Today’s Video of the Day is a performance of the Adagio from Mendelssohn’s Violin Sonata in F major by Emily Sun and Joseph Havlat. Sun plays on the 1753 G.B Guadagnini ‘The Adelaide’ on loan from the ...

View Full Profile. Learn about our Editorial Policies. Most vertebrate skin appendages—hair, feathers, and scales—develop in a pattern dictated by the interaction of functionally opposing molecules.