VARIATION AND DIFFERENTÏATION 189
into vettebræ.
In the words of Sedgwick, the“ number of
vertebræ is therefore an acquired character after the little
larva has been moving about-for some time. If we”think
-
of the notochord as a exible rod moving to and fro with the
working of the muscles, we can readily understand hoW it
becomes broken up into parts "(veeb‘r—æ) aœ‘0rdinglto the
movements and the density of its substance. In agreement
With this view, we nd that the species With longer body,
such as the Herring, display considerableyariation in the
number of vertebræ, whilst the concentrated forms shbw
little or noñe at all.
.
Ï
The inheritance of shesis
one of balanceas well
as of subStance.
The bodies have been tuned through many
generations and thousands of years to move in certain ways,
and it is probably more due to this tuning than to the actual
substance that the species and groups remain more
less
constant.
The balance of the.body and head is the -çontinuæ
tion of the regulating inuence which "can be detected already
in the egg.
It may be said to represent the life of
sh,
and.- this,—'unfortunately,is just; the elementrthat isfnssed
the 'heredity studieswhiCh isoläte one or more characters
,ïrom;the rest and.;take-}no account} of their m0de or time of
Ïf , '} 5
;_,
j =
f
ff"
[
:
-
3.
-
If we examine a large numbeffof eggs
same
_
species or the same specimen, we nd that their sizeïvaries
just like any other character. Heincke and Ehrenbauni
(1900) found by careful and exact methods, that the larger
sh have larger eggs, that the eggs spawned earlier in the
season were larger than
later‘ eggs, and that in
successive groups or batcheS of eggs
“by the'ÏSarne
;
sh the size became smaller. : We thushavea most importantï
—
_
source of variation
the
itis the ;Ï‘ ‘
general
.
’
thesnäa—llé;tgläftà
number of vertebræ
…
of an
,; .
…
_
"
'