THE INHERITANCE OF FAMILY TRAITS 175 



f. Polydactylism. — The peculiarity of supernumerary fin- 

 gers and toes is one that is inherited in nearly typical 

 fashion. I have worked extensively on polydactylism in 

 fowls and there can be little doubt that the character behaves 

 in the same way in man. The extra toe is due to an addi- 



I 



I 



I 



biT. 



_- 11 21 31 4l 

 IV 3P 6N 3P 4N 





12 

 3N 3N 



Fig. 158. — Pedigree of polydactylism. Affected persons reiircsentcd by 

 black symbols. Ill, 3, has six toes on each foot; III, 8, has six toes on each 

 foot; III, 10, extra fingers on each hand; III, 12, extra fingers on each hand; 

 V, 1, five fingers and thumb on each hand; V, 2, supernumerary digits on both 

 hands and feet; V, 5, extra toes, both feet; V, 7, harelip, cleft palate, web be- 

 tween each big toe; V, 10, 5 fingers and thumb on each hand, 6 toes on each 

 foot, web between all toes. Lucas, 1880. 



tional unit so that when one parent has the extra toe the 

 children will also have it. However, it sometimes happens 

 that the offspring fail to produce the extra toe; but such 

 persons, becoming in turn parents, may produce the poly- 

 dactyl condition again (Fig. 158). 



The method of inheritance of polydactyUsm is well repre- 

 sented by Lucas' case, given in Fig. 158. Here only when 

 one parent was polydactyl were there polydactyl offspring, 

 excepting in the progeny of the oldest son of the third genera- 

 tion. This son is said not to be polydactyl and is recorded 

 as normal. If the record is correct his case is one of failure 

 to dominate of the polydactyl determiner. 



The eugenical conclusion is: polydactyl persons will have 

 at least half of their children polydactyl. Those quite free 



