Wentworth: Sex in Livestock Breeding 3] 
as a result of observations on a large 
number of animals, about 3,000, and 
also as a result of a few directed crosses. 
This last spring, due to the kindness 
and cooperation of Professor O. E. 
Reed, of the department of dairy 
husbandry, Kansas State Agricultural 
College, facilities were extended the 
writer whereby another character was 
discovered which falls within this cate- 
gory. The Ayrshire herd bull, Melrose 
Good Gift, is a dark mahogany and 
white in color, what is popularly known 
as black. The occurrence of black and 
white Ayrshires was recently discussed 
in the JOURNAL OF HEREDITY by 
Kuhlman. It is difficult to determine 
whether the dark hairs are due to exces- 
sive deposition of red pigment within 
the hair or whether there is really a 
black pigment. Microscopic examina- 
tion seems to indicate the latter condi- 
tion, but the statement is only tentative. 
When Melrose Good Gift was mated 
to red females, his male offspring were 
all black and his female offspring were 
all red. Nine black males and eight 
red females have resulted from this 
cross to date. Matings representing 
the F, cross are very few, only two being 
available. One black bull and one 
black heifer have resulted. The black 
is the most reasonable expectation in 
the male, but the chances in the female 
would be three reds to one black. Two 
black cows are in the herd and their 
progeny are as follows: one black male 
and three black females by the homozy- 
gous black bull (the expectation) ; two 
black males, two black females, and one 
red female by heterozygous black bulls 
(also the expectation); and one black 
male and one red female by red bulls 
(the same types as in the first cross 
mentioned). Other types of crosses 
exist, all of which supply confirmatory 
evidence for the conclusions already 
drawn. 
SECONDARY SEX CHARACTERS 
The term sex-limited inheritance was 
first used for the secondary sexual 
characters, but its usage has varied so 
that the writer prefers to adopt the 
terminology herein presented. In- 
formation on these characters is classic, 
Darwin having dealt with them in an 
exhaustive manner in the materials 
supporting his theory of sexual selec- 
tion. Sex differences are familiar to 
the livestock breeder, the inhibition of 
their development by unsexing being 
common, and it is doubtful if there are 
any practical possibilities involved in 
this subject that are not already 
realized by the breeder. 
APPLICATION TO PRACTICAL BREEDING 
The breeder’s problem relating to sex 
and livestock is the practical one. It 
can hardly be denied that either form 
of sex-affected inheritance exists, but 
the breeder requires more than. the 
mere existence of a fact to make use of 
it. The study of the individual char- 
acter has shown that its distribution can 
be controlled with little difficulty, but 
no practical means is known of beating 
the old method of mating the best to 
the best, when the large number of 
characters are concerned on _ which 
pure-bred selection is based. In the 
face of Pearl’s remarkable work on 
poultry, it seems ultra-conservative to 
make this statement, but no one has 
yet shown how any of the Mendelian 
knowledge can be applied to the breed- 
ing of Poland-China or Hereford. The 
livestock industry is so much more 
intimately involved with finances than 
with ultimate breed improvement that 
it is not fair to ask any related biological 
fact to reduce itself to monetary terms. 
Some facts have been able to be so 
reduced, but the majority may never be. 
Yet this condition is by no means a 
cause for despair, as the solution is per- 
haps not distant. In the meantime the 
geneticist will continue to contribute his 
quota to livestock breeding, whether his 
contribution be ‘‘linked”’ or ‘‘limited,”’ 
remembering that in the course of the 
world that which is most fundamental 
is ultimately the most practical. 
