Studies on the Mode of Outgrowth of the Amphibian Pronephric Duct

Although the manner in which the developing amphibian pronephric duct extends posteriorly has been studied rather extensively, it has not been clear whether this posterior outgrowth is largely the result of proliferative activity or whether it is due to migration of cells from an anterior level (Cambar, 1949). Holtfreter (1939) has demonstrated a marked migratory tendency in these cells from early gastrula stages in Rana esculenta , but a high mitotic count towards the posterior duct tip has been reported in Triton alpestris (Mollier, 1890), suggesting that proliferation may play a significant role. Furthermore, proliferation appears to be an important factor in elongation of the pronephric duct of the chick (Overton, 1958). This problem has now been examined more closely in a number of amphibian species in the hope that a more precise understanding of the mode of duct outgrowth might throw some light on the question of how the direction taken by the outgrowing duct is controlled.