EFFECTS OF IXBREEDIXG AND CROSSBREEDING. 41 



(6 and 24, respectively). The other produced the 3 other abnormals 

 as well as 10 normals. These abnormals again all came in different 

 litters. Each of the five litters containing an abnormal also contained 

 normals. Only one mating was made in the next generation from this 

 line, and only 3 normal young were produced. The abnormality is 

 evidently hereditary and the data consistent with the view that it is 

 due to a recessive Mendelian factor. The matings of normal to 

 normal produced 26 normals to 5 abnormals. It is quite probable that 

 the abnormality arose as a mutation sometime during the course 

 of the experiment, as it is hardly likely that it would have failed to 

 appear in others of the many lines in this family if the factor had been 

 present in the original pair. Even in this case, however, it is clear 

 that we are dealing with a definite hereditary factor or factors, not 

 with a specific effect of inbreeding. 



The same conclusion applies to another abnormality, the absence 

 of one or both eyeballs. There were 4 of these animals in the control 

 experiment and 11 among the inbreds. Eight were produced by 

 Family 38, 2 by Family 7, and 1 by Family 32. Five individuals, 

 one in each of the Families 3, 11, 13, 31, and 36, were recorded as 

 having one eye smaller than the other. 



The remaining abnormalities were well scattered among the fam- 

 ilies. There were nine with various malformations of the jaws or 

 muzzle. One described as having a ''bulldog face with no upper 

 incisors" appeared among the controls. There were 23 with de- 

 formed legs of various kinds besides those with miniature legs, noted 

 above. Three of this kind appeared among the controls. Ten 

 were described as having a hole in the skull, through which the brain 

 protruded. Three had abnormally large heads. There were 2 in 

 which toes were fused, a variation which also appeared among the 

 controls. Twenty-nine individuals had " mustaches," besides 2 

 among the controls. The inheritance of many of these variations is, 

 is, of course, very doubtful. 



The general conclusion which is suggested by a survey of these 

 abnormalities is the same as that advanced in connection with color, 

 pattern, and vestigial toes. Inbreeding per se has nothing to do 

 with their origin. We find a cyclops, several eyeless pigs, and several 

 head and leg abnormalities among the controls. Whether an abnor- 

 mality appears in an inbred family depends mainly on its initial 

 heredity in that particular respect. One family, as it happens the 

 most vigorous, has the greatest tendency toward producing Cyclopean 

 monsters. Another family produces most of the eyeless animals. 

 Another produces monsters with miniature legs. The two weakest 

 families, in most respects, produce few or no abnormalities. Thus 

 inbreeding can not be considered to be a cause of the origin of abnor- 



