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
Monarch butterfly migration silk moths, Fred Urquart initiated monarch butterfly tagging and used wing incisions, spots arrangements, colored spots, spraying with dyes, painted letters and numbers to mark the butterflies. These methods were unsuccessful as there were no instructions to return the butterfly or record the recovery. Currently, many organizations study migration by tagging. New methods of studying the migration include the use of VHF transmitters and commercial aircraft. Isotopic tagging has been employed. Theories that explain monarch migration are many. "Science has not yet offered a sufficient explanation for how that [the migration] happens." Researchers often propose that multiple migratory mechanisms play