Fig. 2. Schematic illustrations of the water permeability barrier in relation to the stratum corneum of the epidermis in four principal lineages of vertebrates. The images on the left depict the morphology of generalized integument, and drawings to the right illustrate the stylized arrangement of barrier lipids (dark bars) in relation to horny layers of stratum corneum (thin broken lines). The stratum germinativum is represented by the thick broken lines. The features shown are not to scale.