558 
Journal of Agricultural Research 
Vol. XXIII, No. 7 
The following records were kept for each pig: (i) The number of pigs 
in the litter in which each individual was born; (2) descriptions of color, 
set of ears, and shape of face, the latter character being described from 
three different viewpoints—length of face, dish of face, and shape of 
forehead; (3) a diagram of the arrangement of the mammae; and (4) 
growth as indicated by monthly weights. 
The total number and relationship of the pigs produced in each cross 
were as follows: 
Wild X Tamworth: This cross comprised an generation of 38 pigs 
produced in 5 litters out of three Tamworth sows and by two wild boars; 
1 back-cross litter of 8 pigs out of another Tamworth sow and by F x 
boar; and 1 F 2 litter of 4 pigs by the F x boar out of a litter sister. 
Wild X Berkshire: In this cross an Fj generation of 2 litters totaling 
17 pigs was secured out of 1 registered Berkshire sow by the second 
wild boar. 
Berkshire X Tamworth: This mating produced 1 litter of 10 pigs out 
of a Tamworth sow by a registered Berkshire boar. 
Berkshire X Duroc- Jersey: The result of this cross was an F 1 generation 
of 29 pigs in 3 litters out of two registered Duroc-Jersey sows by two 
registered Berkshire boars, an F 2 generation of 151 pigs in 17 litters out 
of 8 Fi sows by an F x boar, 1 F 3 litter of 11, 1 litter of 5 out of an F 2 sow 
by the F x boar, and a back-cross generation of 35 pigs in 3 litters out 
of the Duroc-Jersey sow that was the mother of all the F x animals 
reserved for breeding, by her Fi son. 
There is no a priori reason to assume that similar characters in two 
quite distinct breeds—for example, the erect ears of the Berkshire and 
of the wild hog—are due to identical factor complexes. However, since 
it is more convenient from the standpoint of treatment, each character 
will be discussed in the light of the data from all available crosses. 
INHERITANCE OF FITTER SIZE 
Inheritance of litter size was studied in two crosses (1) wild boar by 
Tamworth sows and (2) Berkshire by Duroc-Jersey. 
It was primarily for the study of the inheritance of litter size that 
the wild hog was used in this experiment, its use having been suggested 
in a previous study by Wentworth and Aubel (23).* This type of wild 
hog normally produces about 4 pigs per litter, the Tamworth 11, and the 
other common breeds about 8 (23). 
Obviously this character can be fully expressed only by sexually 
mature females, and since so many nongenetic factors (23) can operate 
to reduce the actual number of pigs in a given litter below that which 
the sow is potentially capable of producing, it will not be safe to draw 
far-reaching conclusions from the limited data available in this 
experiment. 
Only one Fj sow of the wild X Tamworth cross produced any litters, 
and she produced but one (PI. 1, B). The fact that her litter consisted 
of but four, however, agrees with the results obtained by Simpson (11) 
and is very suggestive of the dominance of the wild litter size. It may 
be considered a good indication that litter size in swine, like fecundity 
in poultry (8 ), is dependent upon certain very definite factors which can 
be inherited in part through the male parent, since whatever factors 
4 Reference is made by number (italic) to “Literature cited,” p. 581-582. 
