So now we are at that dreaded “pharyngula” stage, where we get to consider the similarities in the developing pharynx. “Humans never have gill slits” the creationists will cry, and they are largely correct, but see one exception below. In the pharyngeal region a series of six pouches form (no, they are not just folds in the skin, as some creationists claim). Each pouch contains a cartilaginous pharyngeal arch (which in fish later develops into supports for the gills), and a set of developing nerves, blood vessels, and muscles which have an extraordinary specificity to each pouch and which are homologous among all vertebrates. The clefts between the pouches are what will form the gill slits in fishes.