The programming of canalization in fetal lungs of man and monkey.

In the monkey lung (Macacus nemestrina) canalization of all bronchopulmonary segments begins simultaneously at the peripheral future-alveolar-duct portions of each segment and then continues progressively centralwards. Its simulataneous appearance in all segments of a human lung of the 17th postovulatory week (19th postmenstrual week) has now been confirmed (cf. Boyden, '74). The mode of canalization, as seen under the light microscope, is here demonstrated.