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The ovum of the mink (Mustela vison).

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THE OVUM OE' THE A l l I S K (lIL1STELA VISON)
As part 01;I cooperative study of reproduction iii the miiik
(hIiistela \Tison), made hy lllc 1Siological Sarvey a d the
Clarnegie Institution of Washington, ant1 fiiianccd by BankIicad Joiies ("ooperutii.c Research I'uiids, three tuba1 ova were
recorered and photographed in living condition. The mink
from tvliicli tliese werc' obtained w a s 3 years old. S11c had
refused to mate cliiring her first hreediiig season, and though
she had mated once during hci. second ;vear, she produced no
~ o a n g . Tliis is iiot ail U ~ ~ U S Urecord,
C?~
f o r miilks appear to 1)c
far less prolific either in caapt'ivitv or iii the wild than onfJ
iriiglit expect from a kiio\\~l~dgc
of the common carnivores.
The history of tliis tlriirrial is lmo\vn, f o r she was hrcd at the
s Fnr Animal Experiment Station, riiaintairied
1)) the Biological Survey at Saratoga Springs, Ncn- Toi-k.
1)itriiig hci. tlrircl season she was placed with a male or
m d e s daily fiwm Alurch 9th until Illarch 19th. Vaginal smears
were made daily o r oftener througlioui tliis period. T11c right
orai.y, tlie nteriiie tulle, aiid tlie uterine horn were remored
micler Sembntal anesthesia on March 7 0th. Nine daj-s later
lire sperms were rcco~crctlirom tlic vagiiia. Fifty-tw o hours
after copulation, again iintlrr Xemhutal, the l e f t ovary, 1itc.r.ine tuhe, a n d uterine liorii mere removed. The nteriiic tube
could be s e m passing over llic greatly\. distended capsule that
ericlosed llie 01 ary. Tliis condition hacl derelopecl since the
first lapawtomy.
The ovum ~ v a bfree of follicle cells. The zona pcllnciclu ~ v a s
shai.ply define.cl, relatively iiarrow. I n egg A (see accompanying illustration) the zona appeared to he divided into tlirec
parts, which pliolographecl with considerable distinctness,
possibly due more to optical qualities than to clistiiictive structure. Egg c‘ showed only a slight differeiitiatiori in the zolla,
while egg B was like C’ at a point opposite tlie dark loodies and
Figures A , B and C’
like A elsc~u~1icr.e.The egg proper, o r vitPllns, did not fill the
z o i pellucida.
~
Each egg had a per*ivitt?llinespace filled wit11
granules, r7 conclitioii that appears in all mammalian e g g s
sooil after fertilization.
The cytoplasmic mass of egg d seemed to hc coniiec3tetl to
the zona by a single protoplasmic straid; otliernisc thck maqs
as free -c\ithin the lumen.
471
THE OVUM 011'THE M I N K
I n common with the ova of carnivores generally, so far as
known, the cell mass is very dark because globules of lipoid
material are distributed throughout the cytoplasm. If the
surface of the mass is brought into focus the closely packed
globules are easily observed. The larger granules that lie at
the periphery mcasure about 3 p in diameter. There is no
tendency toward polar accumulation. Two dark bodies appeared in egg A at a tangential focus; similar bodies were
even more clearly seen in egg B. What they represented was
ovux
TOTAL
DIAMETBR
A
B
0.133 X 0.148
C
0.143
0.1.51
DIAYETLR OF CYTOPLAAMIC MASS
: VITELLUS
0.11
0.109
0.103
THICKNESS
O F ZONA
0.011
0.011
0.0113
not determined, though they might be polar bodies. I n all
probability the eggs had been fertilized, f o r sperm heads were
observed in each. While the age of these eggs cannot be
stated, for the processes of ovulation and fertilization in the
mink are not known, studies indicate that they were about
16 hours old.
Many thanks are due to Dr. Carl G. Hartman and Dr.
Warren Lewis, of Cameg-ie Institution of Washington at
Johns Hopkins University, Baltimore, Md., for their very
active aid in making these eggs available for study.
T H B ANATOMICAL RECORD, VOL. 72, NO. 4 A X D S W P L E X E K T
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