CHAPTER IX
,
,
,
THE GENEALOGY or FISHES
'
QUESTIONS of absorbinginterest are always b0und up With ’
the beginning of things. What was the 'oldest sh like?
-
Where was it born ? Every one knows that such questions
cannot-be anSwered with any degree of certainty, yet our
idea Of the present world and the order in which we arrange
the dierent shes, depend On these questions and we must
go on asking them. In the present chapter facts and theories
,
will be discussed in furtherance of this aim.
-
,
…
-,
1. THE OLDES_T FrsHss
,
'
'
'
"
'
'
‘_Fishes-ärehot quite as old as the earth ; the process of
a;1‘m appeared between thelithosphere and
many millions
Even when_iœ _ -
and Water aPpeared—and the temperatures of the AlgOhkian
.
period were perhaps “not so very different fromth0Se of the
present day—organic life had to pass through many phases
,
before the complex substances of a sh’s body could be
_
integrated to hold together. As the heavier and more solid
materials settled down and the water rolled off into troughs
'—
jand'-hollQWS, in great part of its own making, shes were
évolved'in the shallows. Of depths in the sea or heights on ,
-
,
the landin those days there were none.
,
.
,
,
,
The Ïage Of the earth has been computed at a—=Varying,
_
-
number of, million . of, years, according to
estimates of the ; rate of cooling. With
'
the
Of,
-
‘
radium and its _radiant'energy,these estimaitesl'haÿe'îbeen'
'
revised more recently by Strutt
and it'—iS.nOW
—
‘
201
'
,
,'
'
'
,
’'
'
,.
-