The Embryonic Limb Bud of the Urodele:

Scanning electron microscopy and histological investigation of the embryonic fore-limb bud of Notophthalamus (Triturus) cristatus and N. vulgaris has revealed that an apical ectodermal ridge (AER) is not detectable in these species of newt (Urodela). The limb buds examined ranged from those just visible as a slight projection from the body surface through to buds possessing two prominent digits. These stages correspond to the stages in Anurans during which the AER first appears, reaches its maximum size and then regresses. The significance of this observation is discussed.