scales spinulate over a considerable portion of the upper side. The chief
difference between the Baltic and the North Sea is the reduced salinity of
the former, so that it might be supposed that fresher water caused the
greater development of the dermal skeleton. On the other hand, a species
or geographical variety of the Plaice, whose proper is _P. glacialis_, is
found on the Arctic coasts of Asia and America, on both sides of the
extreme North Pacific, and on the east coast of North America. In this
form the bony tubercles on the head in the Plaice are replaced by a
continuous rough osseous ridge, and the scales are as much spinulated as
in the Plaice of the Baltic. On the east coast of North America the males
in this form are more spinulated than the females; on the Alaskan coast,
and apparently the Arctic coast, the females are spinulated, and the
sexual difference in this respect is slight or absent. Lower salinity
cannot be the cause of greater spinulation in this case, and thus it might
be suggested that the condition was due to lower temperature. But we do
not find that northern or Arctic species of fish in general have the
scales more developed than southern species.

The Dab, which occurs in the same waters as the Plaice, has the spines
more spinulated than any of the forms of plaice above mentioned, therefore
the absence or slight development of spinules in the typical Plaice is not
explained by physical conditions alone. Freshness of water again will not
explain the difference of the structure and distribution of scales in
Flounder and Plaice, considering the variety of squamation in fishes
confined to fresh water. Still less can we attribute any of the
peculiarities of scales to utility. We can discover no possible benefit of
the condition in one species which would be absent in the case of other
species. We can go much further than this, and maintain that there is no
reason to believe that scales in general in Teleosteans, or any of their
various modifications, are of special utility: they are not adaptive