Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1915-01-21
DOUBLE-YOLkED EGGS
Some of the Results of Recent
Studies in Regard to Their
Production at Expert
ment Station


naturally and rightly concluded that
they are not unusual. However. We
do not usually consider how many
slnCle-yolked eggs we see to every
one that is -yolked. The Maine
Agricultural Experiment Station flock
| produces 531 single yolked eggs to
every doU BILE yolked egg. That is, only
two tenths of one per cent of the eggs
are double yolked. The ratio of double
to single-yolked eggs is less than twice
as high as the ratio of twin to single
births in the human family.
! Recent studies at this Station show
that all birds are not equally likely to
| lay double-yolied eggs. In fact the
great majority Of birds never lay any
thing but single-yolked eggs. There
are, however. birds which possess a
tendency to lay -yolked eggs.
Such an individual may produce
| several such eggs. 1t has been further
| found that bird which possesses the
| tendency to lay double-yolked eggs
| is not equally likely to produce them
at any age. She is most likely TO pro-
duce them when she is young. Eighty
per cent of all the double olked eggs
produced by the Station flock are pro-
! duteu by pll us 1tsS imam tlSIt IIOltliS
old. We have only very few records
of birds which have laid double-yolh-
ed ggs after their first adult mott.
! 1t has been usually supposed that
/ double yolked eggs are caused by the
simultaneous entrance Of two yolks
into the egg tube and the consequent
common passage of the two yolks
through the duct. A careful study Of
eggs produced by the Station flock
shows that in only a very small 90
Der cent of the cases have the two
yolks passed the entire length of the
duct together In such cases the two
yolks are enclosed in a common thin
layer Of white membrane. the chalazal
membrane, and have only one pair Of
chalazae. They also have COM
mon alhumen envelopes as well
as a common egg membrane and shell.
Since the formation OF each egg part
| {chalazal membrane and chalazae
thick albunen egg membrane, and
SHIELD is confined to a particular part
of the oviouct, study of the number
Of the secondary parts which are COM
mon 80 the two yolks of a double yolk-
ed egg shows the level of the duct
where the two yolks came together.
Such study carried out on all double
yolked eggs produced by the large
flock Of birds owned by this Station
shows that the two yolks unite at
every level of the duct from the mouth
Of the funnel to the very end of the
alburnen secreting portion. 1t shows
further that the number of eggs of
any given structure observed is ex-
actly equal to the mum Der expected on
the assumption that the union of the
two yolks occurs indiscriminately at
every leval Of the duct from the mouth
I of the funnel to the beginning of the
isthmus or egg membrane secreting
! portion. When two eggs unite after
the first egg has received its membrane
the result is two eggs at the same time
The structure q the egg has shown
us that in majority of cases the two
yolks of a douhle-yolked egg have not
passed the entire length Of the duct
together. On a moments reflection we
see that there was never any a nriori
reason for the assumption that the
cause for the production of a double
yolked egg was necessarily the stimuli
taneous discharge of two yolks from
! the ovary into the oviduct or egg tube
| The only condition necessary for two
yolks to he enclosed in the same egg
membrane is that they entered the
membrane secretinS portion Of the
oViduct together. There are at least
three possibilities beside simultaneous
ovulation which may bring two yolks
together before they reach this portion
Of the oviGuct. First, the first yolk
may be delayed at any level Of the duct
forward to the point where the egg
membrane begins to be secreted: sec
ond. the first yolk may be returned
up the oviduct and then come back in
company with the second yolk; and
third, a yolk may be ovulated into the
body cavity and picked up by the
oviduct shortly before or after the
ovulation of another yollz. 1t is, there
fore, unnecessary to assume that the
production Of a double-yolked egg
represents Simultaneous or even an
abnormally rapid succession of ovula-
tons. since any of these delays may
have been as long as the normal
period between ovulations
A study of the structure of the eggs
and the egg records of the birds leads
to the conclusion that double yolked
eggs do not necessarily represent two
| simultaneous or even nearly stimuli
taneous ovulations; but in about enc
third of the cases Of double-yolked
eggs produced at this Station the
time between the two ovulations must
have been unusually short since the
birds which laid these double-yolked
eggs each laid a normal egg on the
preceding day. A study Of the egg
structure of these double-yolked eggs
| where the time between the ovulations
is known to have been abnormally
short shows that the ovulations have
been simultaneous in only a small
per cent of the cases. In fact the two
yolks have come together at every
level of the duct in front of the be-
ginning Of the isthmus.
A study Of the ovaries of birds which
had recently produced double yolked
eggs showed that each of the two
yolks was discharged from a normal
separate follicle exactly as are the
yolks of successive single-yolked eggs.
From these recent studies of double
yolked egg production it is certain that
some individual hens have an inherent
tendency to lay double yolked eggs
while great majority of hens never
Law anything but normal single-yolked
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