288 HEREDITY AND DISEASE 



members had all their fingers and toes two-jointed like the thumb 

 and big toe. The normal members had normal children, even 

 in the case of a first-cousin marriage. The abnormal members 

 married normal individuals, and the fourteen families bred in 

 this way contained 33 normals and 36 abnormals — a close 

 approach to equality. The abnormals are indicated by capitals. 



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Along with defects of parts we may include imperfections due 

 to an arrest of the normal course of development at certain stages, 

 perhaps through inadequacy of nutrition, perhaps because of 

 what we must vaguely call " deficient developmental vigour." 

 Thus, hare-lip is practically the persistence of a normally transient 

 condition, and cleft palate is in the same category. Hutchinson 

 has recorded hare-lip in ten members of a family of twenty. 



Inhibitions or disturbances during ante-natal life are believed 

 to result in various other abnormalities, such as cleft-palate, 

 cervical fistulae (persistence of traces of visceral clefts), spina 

 bifida, certain peculiarities of the eyes and teeth, and so on. 

 These abnormalities occasionally recur repeatedly in a family 

 tree, but it seems probable that what is really inherited is a 

 deficiency in " developmental vigour," accentuated by nutritive 

 defects on the part of the mothers during the period of gestation. 



(b) Multiplicities. — As with defects, so in regard to multi- 

 plicities. Polydactylism has been known to recur through six 





