Heredity 
each line of descent. The result. is, 
that instead of a normal ratio of 107 to 
100 (which was established for this 
particular stock at the beginning of the 
experiment, by ascertaining the sex 
ratio in 1,000 newborn litters), Dr. 
King now gets in various generations 
ratios as far apart as 150 males to 100 
females, in the male producing line, 
and sixty-five males to 100 females, in 
the female producing line. 
If such a state of affairs can be reached 
under the carefully controlled condi- 
tions of a laboratory, it is not a rash 
assumption to suppose that 1t might 
occasionally be reached unknowingly 
in the herd of a practical breeder. 
IN LIVESTOCK INDUSTRY 
Whether such conditions actually 
prevail in the livestock industry cannot 
definitely be told except after thorough 
examination of the records of that 
industry. This would offer numerous 
difficulties. In the meantime, with the 
analogy of Dr. King’s experiments on 
rats, any breeder whose herd sire is 
producing mainly bull calves, and who 
finds that such a tendency marks the 
ancestry of the animal in question, 
might well feel justified in getting a new 
herd sire with a more auspicious 
record. 
Finally, can such a peculiar sort of 
heredity as Dr. King has found, be 
brought into line with what is at 
present known or suspected regarding 
sex-determination? 
There are numerous ways in which it 
can be explained, without resorting to 
anything mystical. Dr. King has not 
yet attempted to offer a definite explana- 
and Sex 1] 
tion, but suggests that it may be due to 
such a simple cause as differences in 
the permeability of the eggs. It will 
be recalled that there are probably 
two kinds of spermatozoa in the rat, 
one of which is male-producing and the 
other female-producing. As these are 
apparently produced in equal numbers, 
it is evident that, since there is seem- 
ingly only one kind of ovum, the number 
of young of each sex produced would of 
necessity be equal, unless some outside 
cause intervenes. 
It is further evident that if the eggs 
of a given female were, for some reason, 
more easily penetrated by male-pro- 
ducing than by female-producing sperms 
then that female would tend to produce 
an excess of male offspring. If the 
condition were reversed, she would 
produce an excess of females. 
It requires no strain of the imagina- 
tion to suppose that a race of rats 
might be developed, in which there was 
a hereditary tendency in the eggs to be 
penetrated more easily by one kind of 
spermatozoa than by the other. If so, 
the sex-ratios which have resulted from 
Dr. King’s breeding experiments would 
be easily explained. 
Whether that is the actual explana- 
tion in this case, and whether some 
similar explanation also applies to 
the cases which seem to have been 
found in cattle and fowls, one cannot 
now say. But regardless of explana- 
tion, the observed facts seem reasonably 
certain, namely, that it is possible fora 
tendency to produce disproportionate 
numbers of one sex of offspring to be 
hereditary in rats, and perhaps in other 
animals. 
1Dr, King notes that she “‘cannot in any case predict the sex ratio in an individual litter, 
since not infrequently the two litters of one female will each contain an excess of males while 
the litters of a sister rat, mated to the same brother, will both contain an excess of females. It 
is only when we take averages for a large number of individuals that we get the results as indicated. 
The average sex ratio for the entire A series is 125 males to 100 females; that for the B 
series is only eighty-three males to 100 females.’’ 
the same direction, in each line, in every generation except one. 
seventh in the B line are the exceptions. 
The deviation from the usual ratio has been in 
The tenth in the A line and the 
