16
'
THE BIOLOGÈFOF FISHES
'
circularto along oval. Further, the edges of the
may
grow unequallÿ, and r0ws of small points then project from
its surface, Which When they harden are sharp and
"
to the touch (ctènoid scale). This roughness sometimes
a0rds a ready means of, distingu—iShing
thus the Dab is- rough, Where the
is_ almost always
smooth.
,_
—
…:n:,—’Ë
'
'
,
Since the scales gr0w With the sh, and the sh grows
uneqüallÿ at
Of the year, the markings on
_
the ‘scales, have beènused ini—many cases to determine the age
of
When the‘sh isgrowing rapidly, as in the spring
and Summer, a “large number of rings or circuli are laid down
in the scale, but as the growth slows down in the autumn
orcèases in the winter, the circuli become fewer in number
and closer' together (Pl. II). These winter rings or annuli
,
,
may thus be said to mark off a year’s growth, though, strictly
*
only represent a certain physiological conof the sh; .
'
.
'
,
,
Ÿ
In favourable
possible to count up to
fteènbf these annuli; but itsmust be admitœd that there is
.
often a great deal of ucertaintÿ in the =matter owingto lack
of deniteness,,which again maybe due to unequal growth ,,
in the summer months.: But On the
scales
_
haVe .proyided a valuabl'e— means of
the ,”rate of '
,
groW‘th in different; years and also
ÇQmPQSiÜOH:—' of
'
Catches from different
,
the
Îhas been, largely employed 1n the international
”Smaîî proportmnof
in any one
_
the,scale will show
as thei‘total of the earlier
_
annul‘i:
from the breadth of the annùlus, it is possible
to ”say Whether the shçhas had a good year
a bad:year of
-
,
: any time in
method has been
.
_deVelo‘pèd Œpeéially by the Norwegian
and
._
Lea.…
:"
,
:'
_.
_
I).n sonne cases the scales are never developed (SiluridS)
_
;
:
may 'rèmainhiddenin the skin, as in
Ï In the