ABSTRACT
The development of the archenteric canal does not make much progress before stage 20. At about stage 20 to 21 the wide archenteric canal becomes dorso-ventrally compressed and narrowed in the future trunk region so that a subdivision into a foregut, a midgut and a hindgut with protruding entodermal mass becomes manifest. The most characteristic feature in the development of the foregut is the formation of the visceral pouches and the oral evagination. The deep penetration of the lateral and ventral blastoporal grooves at the end of the gastrulation process has led to the formation of the ectodermal proctodeum. The formation of the tail bud is reflected in a caudal curving of the posterior portion of the archenteric canal at stage 22, foreshadowing the postanal gut formation and in the ventral displacement of the anal opening at stage 22.
