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194
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: THE-,B—IOLOGY OF FISHES
,
,
4-;‘=
have
ow‘joclean water with a plentiful supply
:
of
above all, they must not be shaken or exposed ï * ' j_'
to rough usage, otherwise weaklings of various kinds arise
and even monstro_sities.
Itmay be said that under natural conditions such causes
of variation would not operate, but that is a mistake.
They
do occur and their production under experiment is proof of
,
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the importance of the inherited environment. Tornier
_
(1908), who has investigated these matters both in shes and ' Ï :
Bat—rachians,_ has indeed suggested the conclusion, that the
:
great Variety of heads and months in different species may
:'5—:
have arisen just from a change in theouter
for
:
example, from shallowto deep water, acting on a constitution
Ï::
notinuredto such conditions. Andwe have no reason to
'Ï
’
believe thatzthe vireaklings would of necessity go
to the wall
.
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underânatural “conditions ; on the ‘contrary, they'might live Î
on
quite different species
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Stronger brethren. This point, however, will _be illustrated
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better under the next section.
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chemiCal
the surroundings in_which an
embryo
is alsb;an important source of variation. ÏÏ," :
_“
(1907) has found that by mixing
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tion
with the salt Water,Ïhe_'was able “l
'ÎÎ0,PYOdUC€' a Cyclqpea_n variety of
This eeCt, ;' ii
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itis pointed out, is dûè'to.the
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the, osmoticï
—_
‘The effectoftheehermcalacüon
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ÇÎ
$©6î6do_ be,
veswleswereenlargedf0rward -
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resulted aria —ïôCtodermïüîleswasalsolaïgel‘ -'zAîthough -
Stkddntthnkmtmtpu had .any
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hdnth11ttpb1thtth d1ff partital
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Wouîdappearmhavenobearmgon—ithe natural
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