Tarantula (Acanthoscurria geniculata) embryo showing expression of genes that pattern the legs and body wall. Right side has curved abdomen, 4 walking legs, and 1 pedipalp (head accidentally removed). Left side has curved abdomen and 1 walking leg (the rest accidentally removed).

The pink/white stripes are where the gene “odd-skipped” is expressed, which marks where the leg joints will form.