scales; but some are almost entirely without them, or have them so
minute as to be almost invisible; as is the case with the eel. The
object of these is to preserve them from injury by the pressure of the
water, or the sudden contact with pebbles, rocks, or sea-weeds. Others,
again, are enveloped in a fatty, oleaginous substance, also intended as
a defence against the friction of the water; and those in which the
scales are small, are supplied with a larger quantity of slimy matter.