:
ï
…
'
"
;
shapes and structures. ,How this has Come about can be
understoo'd from their past history. Each region contains
immigrants'from various
Old and some new,
'
-
with dierent structures to begin with,and these; structures
have then to be adapted :to the, same"condition$,' eVe_nthe
same habits.
For example, the
is
immigrant, into fresh water
'
It has a vent-ral mouth like the Sharks but
,
'
except inthe larva ; it manages to feed by .protruding the
inside of its mouth into aspent—likestructure,
Çarp
and Loach have no teeth either, butthe former haâæpointéd
_
,
snout of the ordinary shape,=whilst the LoaCh has,asuckerlikè mouth with tactile—barbels._ All
in1:he
r
müd.
close by is the Eelliving ina similar
-
it is well provided with teeth. = In all cases the
,,
teeth of the jaws or mouth,' not of the pharynx. ,
ÎÏ
In the ”sea 'We nd thesame phenomenonon a larger— —
scale.
The Rays and F lat—shes are often_found together f—
'
and p'artaking’ of th&same food,;butth‘e , structures,—arevery’
different. ,The,_sàme may
of
,
fÏo;r_theGrey
'
'
; ,ï
,
the'fsamefood,
‘
butagænwmhderentstructures In all
.
,
,
th€old =
'
…
=saaauœsè ,and make ne‘rv‘v-ïones ahkeforasheslt could
”
f
only make small
Forexample,
'
as was mentioned=in Chapter X, the
;
-
lakes of Englandhave gradüally;bæomeSO
.
each lake has its own peculiarraceor eVen species.
;'
best idea of what is and whatis not aan“
furnished bythe coleration of shes.
,
view «this was considered a
,
_
so
Ï _.
"
f f
'
»
-
this view—hæfalhwmdæuseasalreadymentmnedThe
Î
colour 13ap10ductof the metabohsmoftheshonthe one
'
:
hand and
,.