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THE AMERICAN NATURALIST [Vol. XLVII 



With the older boar no evidence of the inheritance of 

 unilateral asymmetry is shown. With the younger boar, 

 however, there is a distinct excess of pigs showing the 

 asymmetry on the same side as the father. Since there 

 is no means of telling from the external appearance what 

 recessive characters the sow may be carrying, it is pos- 

 sible that there is a marked difference in the lateral pre- 

 disposition of the two boars. 



An examination of the offspring of asymmetrical and 

 symmetrical sows shows a slight tendency toward the 

 production of asymmetry in the offspring of that kind of 

 parents. Eighteen sows of this type produced 96 pigs 

 with even pairs and 74 without. Thirty-nine symmetrical 

 sows produced 215 pigs with even pairs and 125 without, 

 Using the asymmetrical pigs as the base, the first ratio 

 is 1 : 1.297 and the second is 1 : 1.72. While we are justi- 

 fied in assuming a degree of inheritance of asymmetry, 

 we are not yet able to show the same by definite units. 



75 Inheritance Lateral or by Pairs? — The embryolog- 

 ical origin of the mammary tissue suggests that there 

 may be a lateral inheritance. In order to determine this, 

 the right side of the mother was correlated with both the 

 right and left sides of the offspring, and the left side of 

 the mother correlated in the same way. The offspring 

 of the two boars were separated, since the old boar had 

 six teats on the left side and five on the right, while in the 

 young boar this relation was reversed. 



The results were disappointing if one expected a high 

 correlation. 



Right side dam to right side pig 1196 ± .0353 .1601 ± .0346 



Eight side dam to left side pig 0384 ± .0353 .2326 ± .0346 



Left side dam to right side pig — .0023 ± .0353 .1436 ± .0346 



Left side dam to left side pig — .0296 ± .0353 .2132 ± .0346 



In the last three correlations in the pigs by the young 

 boar, the probable error equals or exceeds the correlation, 

 and in the pigs by the old boar, the probable error per- 

 mits the correlations to just about meet each other or 



