In most other fishes, the epithelium covering
the filament includes both the afferent and
efferent edges as well as the spaces between the
bases of the lamellae, which is commonly referred
to as the filament interlamellar space (ILS) (Fig.
3f,g). Within the filament, and bordering much of
the filament epithelium, is the large central
venous sinus (CVS) which is part of the arteriovenous
circulation (Olson, 2002, this issue). The
filamental epithelium is thicker than the lamellar
epithelium, typically being composed of three or
more cell layers.