GENERAL ÇHARACTERISTICS
17
latter they do not developùntil the seventh or eighth;yeàr
But even when
absent, and the
do ‘nOt show the annual rings :Very
clearly, it is'still possible
tell the age of a sh from other
structures, thé vertebræ
cases or bones of the gill—
cover (Pl. II), The differèïtfÿarts of a sh are
deyeloped in all‘especiejs,and one has to search f0r-‘the most .!
-—
suitable structure.
" '
;
‘
scales, being formed «of a bOny
_
substance, do not contribute much to the colour,
Wecan
'
readily see on
them fr0m the sides of the Herring.
Yet by reectig the rays ofhght at"different angles, especially
they are large as in
the{yladd tdthe s11very
x
_
or glassy appearance of theÏish.
.
inches across, of the American Tarpon are madeÈ:into
_
_
—
‘
,
The real colouring at—œ; lies beneath-“Ïth<ä
_
_
two layers, an' outer_'and
_
an inner or jdîefeperlayer
8‘),
each consisting: of a large
Ofp1gment—contammg f
cells
chromatophores; "These' are formed from
"
.
'conneetivéf;tiË$ùe cells of
_
—
.
Th 1ungntt wthnnyhdyllw …: and
ipèfhäiäsblu(Zynk)hll kpgtpt1
__
colours result, suchas green— bfî5}œxäf, andvarrogmarkmgs
are formed by'
in thef;amountjand.posîbn of ,
the pigment in the two layers. These chromatophores
have also the peculiar power
of concentfatig or spreading out
'
pigment within thefcell, appàrently by stream 1noyÇämen}t‘s
_,
(Fig._ 8),and this in itself means a change of
if
the chr‘0matophoresare—expangljedandthen
_
-
ÂÏ.Ëfheî r15igmjent
the -'_=Wh01éc appearàfcëjï ”of the "5311
.=ÉïîËÏÈéÏ-ïàgês & blacksp0t “bsçÏëmesa greyâd jthÿe‘ï red: _.0rïyéÿlliqwÿ ;—
_
spots
Or
Th13power 15
'
neweussysternsothatmanyshes …
"
ièolQurs—
HOW—î
th18 is
laterg:ÿÎ
f_Ï"‘Ï
i-‘;;=Ï{;<
‘
,
OWè,fç1ieiweahhofvauab1ecolo…œ