INHERITANCE IN THE FEMALE LINE OF SIZE OF 

 LITTER IN POLAND CHINA SOWS. 



By GEO. M. ROMMEL, B.S.A., and E. F. PHILLIPS, Ph.D. 



(Read October 19, 1906.) 



Among the many problems of heredity yet to be solved, one of 

 the most important is the determination in numerical values of the 

 amount of transmission of different characters, which actually oc- 

 curs. Galton (1897) and Pearson (1900) have given us their 

 determinations of the theoretical correlation between parents and 

 offspring, and several investigators have made mathematical deter- 

 minations of the exact amount of correlation of various characters 

 occurring between parents and offspring to the second generation. 



One of the recent problems of the Department of Agriculture has 

 been the determination of the size of litter of Poland China and 

 Duroc Jersey sows, these results being recorded in Circular No. 95, 

 Bureau of Animal Industry, " The Fecundity of Poland China and 

 Duroc Jersey Sows," by the senior author of this paper. The 

 results of this work may be summarized briefly as follows : " An 

 undoubted increase is evident and the conclusion is inevitable, that, 

 contrary to popular opinion, the Poland China breed has increased 

 in fertility during the past twenty years. . . . The increase shown 

 . . . (is) .48 per litter " (n. litters 54,515). The average size of lit- 

 ter in Poland Chinas, as recorded in the " American Poland China 

 Record " and the " Ohio Poland China Record " for the first five 

 years examined (1882-6) is 7.04, and for the last five years (1898- 

 1902) 7.52. The Duroc Jersey records were calculated from the 

 " National Duroc Jersey Record " for the years 1 888-1 902 inclusive 

 with an average size of litter for the years 1 893-1 902 of 9.26 {n. 

 litters 21,652). These records show no measurable change in size 

 of litter for the period covered. 



With these data at hand, it seemed desirable to continue the work 

 to determine how far this character, size of litter, is inherited. The 

 determination of the inheritance of fertility, fecundity, or number 



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