912 
Journal of Agricultural Research 
Vol. XXX, No 1 
man himself, from the list of eligibles. 
In short, this investigation has not 
strengthened the belief that there is any 
method of controlling sex among the 
higher animals which is practical, 
simple, and of wide application. 
SUMMARY 
Centrifugal separation of the male- 
producing and female-producing sper¬ 
matozoa was attempted with liquid 
recovered by means of a catheter 
from the vagina and uterus of female 
rabbits which had just been served 
by normal males. Other females were 
then artificially inseminated with por¬ 
tions of the centrifuged liquid or with 
liquid treated in other ways and the 
sex of the young thus produced was 
recorded. The only deviation from 
equality which approached statistical 
significance was in the sexes of the 
young produced by females which had 
been served naturally and then had 
had as much liquid as possible recovered 
from the vagina and uterus by means of 
a catheter. There is no evident 
explanation of this result, and since 
the deviation is barely significant 
statistically it is concluded that this 
is probably a chance deviation. 
Microscopic measurements of the 
head lengths of a large number of 
rabbit spermatozoa, both before and 
after centrifuging, show that a dimor¬ 
phism probably exists but that the 
size difference between the two groups 
is very small. It is not certain whether 
centrifuging has had any effect upon 
the distribution of sizes. 
Similar measurements of swine sper¬ 
matozoa have shown the existence of 
a dimorphism in size, but not as great 
a difference as was reported by Wod- 
sedalek. Centrifuging effected a par¬ 
tial separation, tending to throw more 
of the larger spermatozoa to the outside 
of the tube and leaving more of the 
smaller spermatozoa near the inside. 
Sex control by centrifugal separation 
of male-producing and female-produc¬ 
ing spermatozoa seems possible for 
species where the difference in the 
sizes of the X-chromosome and the 
Y-chromosome is a considerable per¬ 
centage of the total amount of chroma¬ 
tin in the spermatozoa. Whether such 
a method can be made practicable 
even for the most favorable species 
depends upon whether the technique 
can be simplified and made dependable. 
There is nothing in this work which 
can be regarded as an argument 
against the chromosome theory of sex, 
but, on the other hand, there is no 
new evidence in support of it. The 
failure to control sex in rabbits mav 
be tentatively attributed to the im¬ 
possibility of refining the technique to 
the point where advantage could be¬ 
taken of the very small difference 
which exists between the X-chromo- 
somes and the Y-chromosomes of the 
rabbit. 
Spermatozoa retained their ferti¬ 
lizing ability as long as 24 hours in 
vitro at low temperatures and retained 
their motility as long as 60 hours in 
vitro at moderately low temperatures 
and up to 200 hours when kept in an 
excised testicle on ice. 
Coition is not necessary to ovulation 
in the rabbit. 
The chances of a female becoming 
pregnant when inseminated were in¬ 
creased by diluting the fluid used, 
but were decreased by holding it some 
time at a low temperature. 
LITERATURE CITED 
(1) Bachhuber, L. J. 
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SOMES AND OF THE CHROMA!OID BODY IN THE 
SPERMATOGENESIS OF THE RABBIT. Biol. Bill 
30: 294-310, illus. 
(2) Bonnier, G. 
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u. Vererbungslehre 31: 153-169, illus. 
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(4) -• 
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(7) -and Davis, C. L. 
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(8) CORRENS, C. 
1918. FORTSETZUNG DER VERSUCHE ZUR EXPERI- 
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