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 Koi fish from competition although their American counterpart the Associated Koi Clubs of America (AKCA) has (as of June 2006) reportedly created new standards for judging butterfly koi at future AKCA competitions. American shows that permit longfin or butterfly koi usually enter them as a variety. These entrants rarely win higher awards, however some shows feature "Best Longfin" under and over 18 inches. Butterfly carp are preferred by many keepers of traditional koi who view the breed as superior to normal koi, although all koi are the result of continuous inbreeding whenever a new recessive gene showed itself over the centuries.