l
.
.
.
_
THE BIOLOGY "OF EI“SHES
Obtained a very largé15erœntage of males _; in Some
indeèd, all Were malesi
_
the condition of the
sex=cëlls_àt the time of fertilisation “fis of the greatest importance.
If the manager of a trout orîSalmon hatchery keeps
the females back until all are ripe
same time, the
chances are that he Will obtain too many males in the
_—
ospring.
'
_‘
'
‘
In other
placed two sets of eggs,
from the same
under different conditions of cold
and warmth.
the former case he obtained about three
males to one female, in the latter only a slight excess
of males.
And he found also that in the
developed from the
cold cultures tfansit‘ional stages from female to male sexùal ‘
organs Were unùsually abundant ; thatis to say,’ individuals
‘
_
which normallyWoüld have been females had turned into
'
,
_
_
_,
Otherexperiments showing the infernce of the chèmiCal
conditions on“ sex—determination have been made by Helen
King (1911). In faintly acid solutions the perc'entage-of
"
males was increased, Whilst in hypert0niC solutions (equal
percentages of salt and
reduced the amount
of water in the egg, the great majority became
:i:”ïÏ
‘These—‘ results clearly indiCate that
variable
character, so îfar as the little
and shes are
,
conCerned.
chr0mosomes may ÇÏ be:fpres‘ent; = but1t fis
probably theinhétéd‘balancè rather than the substancethat
,
of
characters Whatever
'
ups)ets.—this{balaèe
development and
_
altersthestructures
.“
:
Ï‘ Theexperienceoftheïpracücalbreederof aquarium
-
Ç
tells 1nthe Same direction Ina brief "
but interesting
'
notice " Thumm (1908) narraæs ; how the "propertion of» the
:
Ï':’
,_ j;,SÇXÇS becomes exceed1nglyvariablefin‘ man-ÿ tropical she's
-
have} been introduced“ into Eur0pe.
'
.
,
Sometimes
only males (]enynsia), at,
'
:
other times almost entirely females (Molli€rsia); He points
_
,
great deal on the Size-”and
‘
-
»
On
aifenialef of Ï three