1886.] 



Family Likeness in Eye-colour. 



415 



So that each grandparent contributes on the average 0*16 (more 

 exactly 0"1583) to the heritage of M, and the four grandparents 

 contribute between them 0'64, leaving 36 indeterminate, which when 

 rateably assigned gives 0'25 to light and 0*1 1 to dark. A hazel-eyed 

 grandparent contributes, according to the ratio described in the last 

 paragraph, - 10 to light and 0*06 to dark. All this is clearly expressed 

 and employed in the columns II of Tables V and' VI. 



III. Eye-colours given of the two parents and four grandparents — 

 Suppose P to possess r, then P taken alone, and not in connexion 

 with what his possession of r might imply concerning the contri- 

 butions of the previous ancestry, will contribute an average of 0'25 

 to the heritage of M. Suppose G l also to possess r, then his contri- 

 bution together with what his possession of r may imply concerning 

 the previous ancestry, was calculated in the last paragraph as 

 ^.=0 - 07o. For the convenience of using round numbers I take this 

 as 0"08. So the two parents contribute between them O50, the four 

 grandparents together with what they imply of the previous ancestry 

 contribute 0*32, being an aggregate of 082, leaving a residue of 0'18 

 to be rateably assigned as 0*12 to light, and 0*6 to dark. A hazel- 

 eyed parent is here reckoned as contributing 0'16 to light and 0*9 to 

 dark; a hazel-eyed grandparent as contributing 0*5 to light and 0*3 

 to dark. All this is tabulated in Table V, and its working explained 

 by an example in the columns headed III of Table VI. 



Results. — A mere glance at Tables III and IV will show how 

 surprisingly accurate the predictions are, and therefore how true the 

 basis of the calculations must be. Their average correctness is shown 

 best by the totals in Table III, which give an aggregate of calculated 

 numbers of light-eyed children under Groups I, II, and III as 623, 

 601, and 614 respectively, when the observed numbers were 629; that 

 is to say, they are correct in the ratios of 99, 96, and 98 to 100. 



Table VII. 



Number of Errors of various Amounts in the 3 Calculations of the 

 Numbers of Light Eye-coloured Children in the 78 Families. 



Data employed referring to 



I. The 2 parents only 



II. The 4 grandparents only .... 

 III. The two parents and 4 grand 

 parents 



Amount of Errors. 















Total 



o-o 



0-6 



12 



1-8 



2-4 



Cases. 



to 



to 



to 



to 



and 





0-5. 



11. 



1-7. 



23. 



above. 





19 



30 



18 



5 



6 



78 



16 



28 



10 



10 



14 



78 



41 



17 



8 



4 



8 



78 



