AND DIFFERENTÏATION
173
The characters of a sh are Of two kinds, those— that can
be counted and these that have to be measured. The
former, such as the number of vertebræ, remain constant
for the most part throughout life, whereas the measurements,
'
for example of the head and body,
the growth. The former can also be "more=exaCtly°d€tèr—
r'r1ined, With a'smallerpersonail error, than the flattefl:.iFor
these reaSons there has been a tendency of recent yeàrsto
n‘églect the meàsurable' characters altogether.
-
a -mistake.g It means thatthe form or Shape of the sh'is
ignored, a character Of the greatest biological importance,
Whilst the conclusions drawn from the numerical characters
alone become one—sid“edi
'
"
‘
,
Some of the characters of shes Varyonlÿ a little; ' The
caudal n remains very constant b0th in form and number
of rays,
only in a species but even Within wide groups.
.
It is the most specialised part of the body, being adapted to
a particular mode of movement. Even the number of verte'
_
bræ may become very constant, as Will be noted later; 7ŸBut
apart from these—special cases, it may be said
all
.
charaCters Vary a good deal, so that one individual cannot
be taken; to represent the species or
The number
"
of Vertebræ 1n
for example, varies
to
'
44;
not} be cOrrect, therefore, {to, saythat"
,
has 42 vert'ebræ.
An average has to
taken, and
,
'
then we find that this average varies
region to
another and even from one year to
ThuS, by a
—;—
simple arithmetical calculation we obtain a
insight
,
into biological problems.; }Thè' variation of one .or* two
indiduals'nght
C°l‘ casual ; _. Ïth—Ô
'
uctuat1on of a«largefnumber at once "indicates the presence
_
0fr€gular causes
f
..
'
'
,
In “the study of
_'
so fthät*thè cumbersome
_'
made_g>':'Èrèvèàli
'
’
SeCr_ets.
_;
’
_
length
so on,themeasurements '
';
are.ïeîpressed,
173
The characters of a sh are Of two kinds, those— that can
be counted and these that have to be measured. The
former, such as the number of vertebræ, remain constant
for the most part throughout life, whereas the measurements,
'
for example of the head and body,
the growth. The former can also be "more=exaCtly°d€tèr—
r'r1ined, With a'smallerpersonail error, than the flattefl:.iFor
these reaSons there has been a tendency of recent yeàrsto
n‘églect the meàsurable' characters altogether.
-
a -mistake.g It means thatthe form or Shape of the sh'is
ignored, a character Of the greatest biological importance,
Whilst the conclusions drawn from the numerical characters
alone become one—sid“edi
'
"
‘
,
Some of the characters of shes Varyonlÿ a little; ' The
caudal n remains very constant b0th in form and number
of rays,
only in a species but even Within wide groups.
.
It is the most specialised part of the body, being adapted to
a particular mode of movement. Even the number of verte'
_
bræ may become very constant, as Will be noted later; 7ŸBut
apart from these—special cases, it may be said
all
.
charaCters Vary a good deal, so that one individual cannot
be taken; to represent the species or
The number
"
of Vertebræ 1n
for example, varies
to
'
44;
not} be cOrrect, therefore, {to, saythat"
,
has 42 vert'ebræ.
An average has to
taken, and
,
'
then we find that this average varies
region to
another and even from one year to
ThuS, by a
—;—
simple arithmetical calculation we obtain a
insight
,
into biological problems.; }Thè' variation of one .or* two
indiduals'nght
C°l‘ casual ; _. Ïth—Ô
'
uctuat1on of a«largefnumber at once "indicates the presence
_
0fr€gular causes
f
..
'
'
,
In “the study of
_'
so fthät*thè cumbersome
_'
made_g>':'Èrèvèàli
'
’
SeCr_ets.
_;
’
_
length
so on,themeasurements '
';
are.ïeîpressed,