‘
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180
THE BIOLOGY OF FISHES
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water, the direction of the aXes and curves would give a r
'
measure of thè""felative speèds. Thus, a"Sharp—nüSed sh
darts through the water, a blunt—nosed sh is slow in its
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"
movements, and between these lie many degrees. HenCe
'
'
angle of the co—ordinate axes increases with a decrease" Ï
"in'the Speed.
.
a
_
An example of the use of the method is given in the
j
accompanying gures.
Changing the straight lines Of
,
”
,
‘Scarus into appropriate, co-axial circles, we obtain the
_
form of Pomacanthus.
But if we could express these
â
,_
relations dynamically instead of statically, thus, by starting
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'
fror' the centre of movement near the tail (see Pl.___Xa.)
*
;
and representing the lines of force acting through the—body
forwards and backwards, with a corresponding system of'
'lines representing the pressure and resistance of the med‘iuï,
we should probably obtain an even better picture of the
'
ï
form—variations in shes (compare Fig. 21).
_
_
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'
_' 2. HEREDIT_Y AND CÏRCUMSTANCES
The small variations shown by the characters of a sh
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thus agree -more or less closely with the laWs of chance
_- occurrences.
The. question is now, whether We know the
7
ways of nature sufciently to be able to eliminatethe word
"»
"
“
chance.”
"
Astone may be rounded or poited and nine
people out of ten would give a
the
dierêCe ; in the case of ?
be
dilcult,to nd two peopléin—tëWho'wouldëägree as to the
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that—thesecannotbeïdet‘ermined, it is rather
because ”chère
arfd
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:
as
make alloWànëëä' f0r
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ÎÏ -'“
—
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'.
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.
The
vary; “Or Variability, is inheient in the nature Ï' —_*
oforgamc subSt‘ancesï "”We may mix the same-ingredients
the-same way, yet a slight dierence ini Ïthe
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Î
temperaturedurmg the : xin‘g“
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Will
-
Î :__—_; pounds, the'ï'n‘ôlecu1ar
not
Even
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:
if we have the same compound, it ‘vvillîgiot' behavein
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