The lamellae of lampreys and higher fishes are
produced by cross-folding (perpendicular to long
axis of filament) of the upper and lower sides of
the filament epithelium (Fig. 2). The lamellae are
in evenly spaced rows along the length of the
filament (Fig. 2, 3f,g), although in the elasmobranchs
they are at an angle slightly oblique to the
long axis of the filament (efferent edge closer to
the pharynx than the afferent edge).