74
THE BIOLOGY OF FISHES
throw—on the future differences between the various groups
of -shes.
The nervous and vascular systems of the Teleosts
are inferior to those of the Elasmobranchs, and the digestive
-
tract of the former ret‘ains throughout life the tendency
.
to be a respiratory organ. » The Ganoids and Dipnoi are
in this respect, whilst the Elasmobranchs show no
'
sign of it at_any time.
_
.
-
'
3. LARVA AND POSTLARVA
.
_
'
.' :
With the termination of the embryonic life the dominance
‘
of the constitutional inuences comes to an end.
The larva
'
now. comes into direct contact with the inherited environ—
ment
its movements henceforth are responses to stimuli
Î’
from the *surro'undings. Its further growth is therefore
determined as much from Without as from within.
:
.
*
*
The free—swimming larva‘of the T’eleosts. is still efnbryonic
'
in its characteræd carries
the yolk—food-givenîit by
its parent for some time, quite“ as long'as the
_
7
the ’egg. As it is a free-swimnng form, hoÿVeVer,ÿWiær—nus_t
;
call
and
Word has béencoi_ñëd forthè later
*.
*
‘
the yojlk: has been
This is- the most
—
important
the life
the Teleost, when bony
substance appearsaändmany transf0rmatio‘ns take place.
.
ï
'
to use the
”
forthe
,
stage;
-
'
call the
a—HtthpltgFth: emphasises the
*
umquechatacterefthereosts
:
_
.
.
'
’
—
î
the =._errrbr‘yo on
.
}
:
7
'J'hafChi'g
on the
Ï
Ï
{amount
freedom…forsmoire—
,
_
.
mentmf ‘ÎfheÏfesgï ÎL Thie—Çësïisvélorämenët%réäëhës :.îfs., highest
-.
Ÿ’Ÿ
; ‘ ”Point—a Where; .b0thÿëareï
;
: '
'
_1_' E
eXte_nt
*
:
:
accumulation :o£jyq1kj—hasehad its disadiäanragès,
2 1 when
1 3,15) In s;pitegof; '
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5