4…
THE BIOLOGY OF FISHES
cardinal difference from the worm. Its organising and
Controllingfacultie‘s are central—ised instead of diuse, and
it
has more mastery over its surroundings.
Yet it has —to be noted, that the simplest form of “ sh ”
known—th‘oughlit' may be a degenerate—has little. more
brain or sense organs than a_ worm and lives almost like a
'
“
:.
,
,
’
_
'
_
-
The older, and still the popular, idea of a fish as a being
that moves thrOUgh the waters is the oriethat shouldbe kept
m03t in mind.
just as ight is
the outstanding‘Characteristic
'
of birds, swimming is what we associate most naturally with
a sh.
We shall be obliged to modify this idea somewhat
as We go on, for most shes, so far
of types or
species is concerned, have eased off= in their swimming
_
inclinations and a ‘feW hop about on land—rennding us
that in the distant past some kind of frog emerged from
the water and learntthe lessons which made higher vertebrates possible”; but of the total numbers of shes most
remain, as they were in the beginning, Creatures that live
and move in the sea.
,
»i
'
_
'
,
z. FORM AND MOVEMENT OF FISHES
:
_
.
Theideal shis,then,onè that cleaŸes the water. In Shape
'
it is like a spindle, or rathera torped0,with the
__
_.
‘
_
.
_
_
_
,
_
FIG 1_———The Herring
êîîËus) M.
gt, gill—ëbver
.
,
n.;
n, ,c.—,=caùdalnD_=.»,_ dorsaln._
_
_
_
_
_
_
,
u—n'derthé'
'
,.
aeross"the-'shOùlders‘of“p€ct0ral region,— then the
_
_
depthandthiCkeä'ss
toWards the tail;
Thé
,
;