CHAPTER X
_
DISTRIBUTION OF FISHES IN TIME AND SPACE
'
FROM the considerations given in previous chapters it is
:
possible to draw a biological picture, at least in outline, of
'
the distribution of shes in the past and present.
For this? '
purpose it is convenient to group the geological epochs
—
'
into two” divisions, one reaching from the earliest times
'
down to the great cataclysms in the beginning of the
ë
_
period, the other overlapping this somewhat and extending
from theChalk period down to modern times. As central
:
theme we may endeavour to trace the fortunes
.
of the
pelagic, free—swimming type, “its changes in form and
.
structure down through theages and its various experiences
_:
under dieret conditions Whilst the face of the Earth was,
Ÿ also changing.
'
'
,
,
1. ANCIENT Pmærons
_
.“.
_,
'
:
.
The land—masses of those early Palaeoz‘oic
days have to be
from
_thos'e we know at prè$et: Thelandwasprobably10wand j
,
'
comparatively: uniform 1nhe1ghtWhetherthemasses
;
Were, all
now, With land—
Î
;
‘
is not of much
=
_
_
importanceto;bëgin,_With., In either case we must suppose
f
;
by the land were in places saline,
'
is _quite possible even in land-locked seas.
f
Ê
this point becomes apparent when we
:
cons.1derthe' actual Origin of shes. It is the
,
general.
È
’
a11 life; includingshes,began'in the sea.
—Ï'
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