How the Snake Lost Its Legs fly embryo. His books on evolutionary developmental biology (evo-devo) include "Imaginal Discs: The Genetic and Cellular Logic of Pattern Formation" (2002), "Quirks of Human Anatomy: An Evo-Devo Look at the Human Body" (2009), and "Deep Homology? Uncanny Similarities of Humans and Flies Uncovered by Evo-Devo" (2017). In Held's view, "Quirks", "Snake", and "Deep Homology" form a trilogy on evo-devo. "How the Snake Lost Its Legs" is ostensibly organised into six chapters, but in effect into three parts. The first chapter serves as an introduction and overview. The next four chapters provide what Held calls "the meatier aspects of evo-devo" with
Butterfly kick used defensively to evade an opponent's floor sweep and land on the enemy's vulnerable side. There are many variations, and different movements may be captured under the same name or likewise similar movements given under a different name depending on the martial arts school or style. It can be executed either from standing or from a step up run. The name "butterfly kick" is due to the legs reaching the apex of their arc the arms are stretched out, leaving all limbs extended in a position similar to that of a butterfly's wings in-flight. There are many butterfly kick variants,