[A morphological study of the apical epidermis during early limb development in anura].

1. The hindlimb buds of AnuraAlytes obstetricans, Bombina variegata, Rana temporaria, Ranma esculenta, Bufo bufo andBufo calamita were investigated for the presence of an apical ectodermal ridge using histological techniques and dry preparations. 2. In all six Anura species an apical ectodermal ridge was found to be present. The ridge ofAlytes obstetricans, in particular, is comparable with that of Amniota. 3. InAlytes obstetricans, Rana temporaria andRana esculenta an increase in cell layers and development of basal columnar cells leads to the formation of the apical ectodermal ridge, while as inBufo bufo, Bufo calamita andBombina variegata the development of the basal columnar cells alone forms the ridge. 4. The apical ectodermal ridge exists from the stage when the limb buds are approximately the same length as breadth until the beginning of the digit formation. 5. With the exception ofBufo calamita the apical ectodermal ridge extends asymetrically over the apex of the limb bud being longer on the preaxial side. 6. The marginal vein is only visible after the ridge development has begun. It underlies the ridge in the mesenchyme one or more cell layers beneath the basal membrane. 7. InRana temporaria andAlytes obstetricans an increased percentage of pycnotic cells is found within the ridge during a particular period.