250 PRACTICE OF POULTRY BREEDING 
new blood of the same breed. It is usually done with two objects 
in view: (1) To correct some defect which it is apparently impos- 
sible to correct within the line which has been established and fol- 
lowed; or (2) to introduce some desirable feature which the estab- 
lished line does not possess. 
If careful selection has been made in line breeding, it is doubt- 
ful if out-crossing should be resorted to except for one of the above- 
mentioned reasons. Even under these conditions, out-crossing 
should be cautiously done, lest the variations which are produced 
follow a different line or direction from that which is desired. 
Reciprocal Crosses.—By reciprocal crossing is meant the alter- 
nate crossing of male and female of two different breeds or varieties. 
The behavior of reciprocal crosses in poultry breeding is an inter- 
esting phenomenon. When two races of the same general type 
and character are crossed, the progeny are similar, no matter which 
type was used as the male parent. If, however, the parents are 
widely different, the resulting progeny will vary with the'varying 
size of the parents. For example, if one parent is a bantam and 
the other a large bird, the size of the egg, and therefore of the 
chick, will be like that of the mother. If the mother is a bantam 
the chicks will be small; if the mother is of full size the chicks also 
will be full size. There are many minor features which give similar 
results, but generally the progeny resemble each other regardless 
of parent alternations. 
Control of Sex.—A problem concerning which there is much 
speculation and discussion is the possibility of controlling sex. 
From the standpoint of economy and profit, it would be a great 
advantage in poultry breeding to have a large majority of the 
progeny females, since one male is sufficient for a considerable 
number of hens, and the female is the real economic producing 
unit. Despite the fact that numerous rules have been formulated 
for controlling this factor, our present knowledge of the laws of 
reproduction does not permit us to expect any great variation in , 
either direction from the usual 50 per cent of each sex. Sex is 
undoubtedly determined, in birds at least, at the time of fertiliza- 
tion by the union of certain kinds of germ cells, and its control is 
at present beyond human power. The sex of the egg after being 
laid is not known. 
Summary of Breeding Systems.—Considerable has been said 
concerning different systems of breeding. The choice of a method 
should be governed entirely by the purpose to be accomplished. 
