VARIATION AND DIFFERENTIATION
193;
The results thus seem to be contradictory or patadoxicàl,
and we nd much the same thing in nature. The species
of the same group living in the tropics have a lower number
of vertebræ than those of the temperate zones, and in general
the number of vertebræ increases towards theçpoles, Yet
there are exceptions. The question is,
the temperature does really operate in two diereht;wzin or
whether other factors are concerned in the matter? :
Ÿ
,
The
perhaps be understood in the following
manner.
An increase of temperatUre undoùbtedly,heightens
the
metabolic processes and leads to greater: activity
internally.
are hàtche‘d out sboner under
high temperatures,ÏbUt aren0t so wellèdeveloped as under
'
low; theïlarya— is ’Smaller with more yolk to beàbsorbe‘d and
,_
the internal tissues are less di‘erentiated. Hence, where a
difference of temperature Operates on the eggs, the higher
temperatures should lead to a smaller number of vertebræ;
_
But the conditions are altered when the different-temperaté
tures operate on the hatched—‘out larvæ—; the
and
mOVements of 'thelatter.haverto be taken- into
: _ *
'
That the Trout Hatched but— under
have;rhë
of Vertebräe is
_
_éqmpfehensi-b-legîànd-it is possible that’the highest
turelhasso inuenced the larvæ‘tjhat they regained_ what they ,
lOst in the
is by means
their;oan
so that they come to have a higher number
-
those under the intermediate temperatures—, though” they
do not regain all that was lost by comparison with those
that remained under the lowest temperatures all the time.
this may be, it is certain that these experiments
of ] ohs-. '
Schmidt, on the inuence of external
’
“
Begin. to ”throw'à ood of light On the complicated questions
of the Origin and differentiation of sheS—indeed, one-may
’
—
say,
in— general. It is not only temperature,
hoWever,” Which leads to variations, During its.ÿperiod in .
7
the egg the embryo is exposed to many
It has bee-fbundin'the Tfout andiSalmon:hâteh6rieS}ithat
.
the greatest cafe must
of
_
_
a
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