26 INHERITANCE OF COAT-PIGMENTS AND COAT-FATTERNS 



has for our purposes little significance, since the parents are selected indi- 

 viduals, while their offspring are not. The same may be said of the coeffi- 

 cients of variability for the parents. For the offspring, the coefficient of 

 variability (ratio of standard deviation to mean, times TOO) decreases slightly 

 in Series D, and increases in Series H. This must not be interpreted as 

 signifying a change in variability of an opposite nature in the two series. 

 It is due entirely to the changes in the mean (average number of spots), 

 these changes being opposite in nature in the two series. If the mean re- 

 mained constant throughout each series, the amount of variability indicated 

 by the coefficient of variability would likewise remain constant ; for we have 

 seen that the standard deviation is constant, irrespective of changes in the 

 mean and irrespective of the number of generations during which selection 

 has been in progress. Standard deviation is, therefore, a better measure 

 of variability than the coefficient of variability in these series. 



The coefficient of correlation (r) has little real significance in tables 26 

 and 27. This constant is relatively small in the Dutch-marked series and 

 grows smaller as selection progresses, whereas in the head-spot series it is 

 relatively large and grows larger with the progress of selection. Selection 

 does not have an opposite effect in the two series upon the inheritance of 

 a coat-pattern. The whole effect is due to change in the amount of the 

 pigmentation, not to its distribution. When the amount of pigmented 

 surface is small, its distribution in certain spots (head and rump) is more 

 certain and the correlation rises (Series H). When, on the other hand, the 

 pigmented surface is large (Series D, table 26), its distribution is less certain 

 and the correlation is low; it becomes lower as the pigmentation increases, 

 in spite of progressive selection. 



The statistical analysis confirms the conclusions previously drawn from 

 our observations. Selection is powerless to fix a particular coat-pattern 

 not dependent upon amount of pigmentation. It is as powerless to decrease 

 the variability in number of spots as to fix any pattern formed by them. 



NOSE-SPOT SERIES (SERIES N). 



It is only in the case of the nose-spot series (Series N) that we are able to 

 detect influence of selection in fixing a pigment-pattern among guinea-pigs. 

 Two individuals showing this rather striking variation in pattern were figured 

 by Castle (105, pi. 6); another 'is shown in pi. 2, fig. i, of this paper. The 

 starting-point of the series of selections for the fixation of this pattern was 

 the male 1989 shown in fig. 12, pi. 6 (Castle, 105). Besides the nose spot 

 shown in the figure, this animal bore a distinct right shoulder spot, not 

 visible in the figure. This animal produced a considerable number of young 

 with nose-spot markings similar to his own, as will be seen from an examina- 

 tion of table 28. As a result of matings with animals which did not bear 



