VARIATION AND DIFFERENTIATÏON
197
who.has endeavoured to furnish any weighty evidence in
its favour, so far as the shes are concerned, is Georg
Duncker. He found that during the transport of living
Flounders from one place to another, the mortality was
much greater «among the sinistral forms than amohgthè
dextral.
Similar experiments with othershes_madèin the
United States have shown that the mortality is much grêa—tcf
among males than females.
In Flounders from the Holstein
coast Duncker found that 36 per cent. of the specimens under—
,
10 cm. were
but in specimens over 20 cin. only
.
25 per cent. were sinistral. Similarl‘y, in a large collection
(1 120) from Plymoùth the percentage of left—eyed specimens
,
decreased With the size (or age) and the selection Seemed to
affect the females more than the males.
'
.
'
In the case of Sÿngnathus typhle a similar investigation -
led to a curious result.
The number
'
of dorsal rings
increased apparently in the adult specimens, that is, the
smaller numbers or frequencies had been more eliminaæd:
'
But this result only held good forthe Plymouth and Bâltic
specimens; specimens from Naples Showecl the
'
reVer'se
.
ç0nditi011,—ailarger proportion'of the smaller frequenCieSLj
,
The
is : obviously too nieagre to permit us .to
form any jùdgmént withçregard to; the practical importance:
of natural
An eli'mination of
not
the same thing as the f0rmatio‘nÏOf species;
in the theory could provide similar evidence on a larger seale_,
weshould be in a better position to judgewhether it is more
than a metaphorical way of descfibing the phenomena of
life.
,
_
'
,
‘
The diiculty of conceiving how species become marked
.
one another in what “appears to be a continuous
region, is more aphysiological than a physical one in the
case of shes.
month of the year has, its own set Of
variable
and
tion of the
Further”,--the_ conditions in the
'
depths. are not
ConditiOns leading
_
_
tion are the—reforealwäys present; and if we consider.a genus ;
such as Aroglossus or Pleuronectes we ”seehowthe species
197
who.has endeavoured to furnish any weighty evidence in
its favour, so far as the shes are concerned, is Georg
Duncker. He found that during the transport of living
Flounders from one place to another, the mortality was
much greater «among the sinistral forms than amohgthè
dextral.
Similar experiments with othershes_madèin the
United States have shown that the mortality is much grêa—tcf
among males than females.
In Flounders from the Holstein
coast Duncker found that 36 per cent. of the specimens under—
,
10 cm. were
but in specimens over 20 cin. only
.
25 per cent. were sinistral. Similarl‘y, in a large collection
(1 120) from Plymoùth the percentage of left—eyed specimens
,
decreased With the size (or age) and the selection Seemed to
affect the females more than the males.
'
.
'
In the case of Sÿngnathus typhle a similar investigation -
led to a curious result.
The number
'
of dorsal rings
increased apparently in the adult specimens, that is, the
smaller numbers or frequencies had been more eliminaæd:
'
But this result only held good forthe Plymouth and Bâltic
specimens; specimens from Naples Showecl the
'
reVer'se
.
ç0nditi011,—ailarger proportion'of the smaller frequenCieSLj
,
The
is : obviously too nieagre to permit us .to
form any jùdgmént withçregard to; the practical importance:
of natural
An eli'mination of
not
the same thing as the f0rmatio‘nÏOf species;
in the theory could provide similar evidence on a larger seale_,
weshould be in a better position to judgewhether it is more
than a metaphorical way of descfibing the phenomena of
life.
,
_
'
,
‘
The diiculty of conceiving how species become marked
.
one another in what “appears to be a continuous
region, is more aphysiological than a physical one in the
case of shes.
month of the year has, its own set Of
variable
and
tion of the
Further”,--the_ conditions in the
'
depths. are not
ConditiOns leading
_
_
tion are the—reforealwäys present; and if we consider.a genus ;
such as Aroglossus or Pleuronectes we ”seehowthe species