MULTIPLICITIES AND MALFORMATIONS 289 



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 

 generations of a human family. Bedart records quadruple 

 polydactylism of hands and feet through three generations of a 

 Perigord family (C. R. Soc. Biol. Paris, gth series, vol. iv. 1892, 



Fig. 28. — Half-lop rabbit, an abnormal variation, which by artificial 

 selection has become a stable breed. (From Darwin.) 



p. 367). Lucas cites a case of a Spanish family which included 

 forty instances of polydactylism, and Pliny tells of si milarly dis- 

 tinguished families in ancient Rome. Hereditary polydactylism 

 is well known in cats. 



(c) Malformations of Parts. — There are records showing the 

 hereditary recurrence of abnormalities in dentition, in the eyes, 

 in the hands {e.g. webbed fingers), in the feet {e.g. club-foot) 

 — indeed, in most parts of the body ; but in most cases the likeli- 

 hood of transmission does not seem to be great. 



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