Mitotic Pattern in the Chick Pronephric Duct

By means of a variety of ingenious experiments it has been shown that the pronephric duct originates anteriorly and grows caudally to join the cloaca (for review, see Burns, 1955). It has been concluded on the basis of histological study (Lillie, 1919), and from operative experiments in which the pronephric duct path was blocked by grafts (Waddington, 1938), that in the chick the pronephric duct extends posteriorly by proliferation of its own cells. In the present study, the proliferative pattern in the outgrowing duct of the chick has been examined in normal and in colchicine-treated embryos. Results indicate that proliferation is particularly marked towards the posterior duct tip. It was also noted that tensions of the blastoderm (see Spratt, 1956) which are disrupted by colchicine treatment appear to play some part in maintenance of normal diameter and posterior elongation of the duct.