58
THE BIOLOGY OF FISHES
mystery in the case of birds, another of the
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few groups of animals that showextensive migrations. In
the words of Prof. ]. Arthur Thomson, these are due to
rhythms and impulses
”
and have nothing
to do With the movements in search of food.
They have
[ :
arisen fr0m the diiculties presented by the seasons in certain
'
,;
areas and take place every year, even the yearlings taking
part. Fromthe experience of many generations birds have
learnt to .evadethe dangers of the Winter at their breeding
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places. They have adapted themselves to the prevailing
lŸ"FIG.
of its life ;
:
.»
below_a-Qlass9Eel—îin
enter.fresh water,
All natural
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Slze(Ff°mï°hSS°hmldt>
:
;
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conditionsletussaybymeansofthemnælhgence and the
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; ma1npr0blemlnCOnnecüonWiththe‘ï‘birds‘ is the manner - _1;
bywhIChtheydthelrwaÿ0‘6tthousandsofrmlesof
,
landandsea
,
shes inay'Ïäappearÿf—the isa—me
'
màtt‘e‘rs.
_
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fÎ:
Theyarenotseasonalmlgratlonsm thesame sen86and the
young takenopartinthem Fishesllavenothing to fear
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i_i j}bç_‘çh Ethe?
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