The reopening process of the esophagus in the normal chick and the crookedneck dwarf mutant
In an earlier publication (Allenspach & Hamilton, 1962) an account was given of chick esophageal development and histogenesis up to 10 days of incubation. The esophagus becomes completely occluded at 5 days (stage 26, Hamburger & Hamilton, 1951) and reopens rapidly at 7½–8 days (stages 33–34). Detailed observations were made of the histological changes in the organs as correlated with the localization of ribonucleic acid and alkaline phosphatase. The occlusion of the developing esophagus was apparently due to collapse and adhesion of roof and floor epithelia to form a solid epithelial bar and not to cell proliferation, as stated in Lillie's Development of the Chick (Hamilton, 1952, pp. 384–5). This process was the object of further investigation in which the role of proliferation in occlusion was determined by the use of colchicine. Results indicated that cell proliferation is not involved in the closing process (Allenspach, 1964).