260
THE BIOLOGY OF FISHES
‘
'—
natural selection point of view—seems too slender an
'
'
hypothesis to suit the facts.
.
'
Gudger (1905) has given an excellent example of nature’s
disregard of theories. As .mentioned above, the Sting-ray
'
is provided with a powerful spine in its tail, which may well
be called an adaptation, useful to and used by the sh. Yet
even this terrible weapon cannot save it from an enemy
that
,
_
ignores spines. In one specimen of a Hammer-headed
_
Shark (Zygæna) no fewer than fty broken spines—repreè
senting about so many individuals—were found embedded
_
:
in the muscles and sticking into the throat (Ehrenbaum,
1915); This Shark, at any rate, was not killed by something
1
far more formidable than a Diodon.
'
It is of interest to note how the development of one
'
adaptation leads to others. The vertebral column of
is an adaptation toîrapid swimming, and in trying ,
to'.attain this end some
_fthe—faimly’have their mouths and
,
_:
tails transformedin various ways. . The Sword—sh and the
Trichiurids are examples which have already been men-.
tion'ed.
A still more striking example is provided by the
(Histiophorus)with their high dorsal n, higher
_
than the depth of the body. It is clear thatSuch a n is out
f 5
of place ina rapidswimmer, yet it has probably arisen just
from the rm and solid looking of the vertebræ. Such a
"
n Would readin be torn in pieces, if the vertébræ were
exible.
Having developed, it is probablyof
p‘re,
'
venting the sh from rolling when sw1mm1ng ‘;at
paCe, but we
doubt whether itis -of ayfuSe‘
'
_ThepeCulia—ruse of
'
and
.
Dactylopter‘us) is
of a similar
kind. The nsWerenot madetoy, _l' they Were an old“
established organ—put
The mode of
;
'
acquiring the new:organis clearly illustrated by the Flying
_ Ï ,
The
have broad pectorals,
_
of moderate‘but‘not exceSsive length. The young Flying
*
-
;
—.
similar
grow older the -
as a Wing,
longer until it
_
_
.—
the body