306 BULLETIN : MUSEUM OF COMrAllATIVE ZOOLOGY. 



occurred along with the atrophy, partial or coinplete, of the functional 

 digits, which apparently caused the subsequent development of the 

 normally rudimentary ones. In these instances it would seem that the 

 nutriment which is normally appropriated Ly the functional digits is 

 transferred to, and utilized by, the digital rudiments, tlius enabling 

 them to continue their development. We are familiar with the same 

 l)]ienomenon in plants, where, if the terminal bud is removed, lateral 

 buds, which would otherwise have remained dormant, are stimulated 

 to development by the extra supply of nutriment which they receive. 

 Again, polydactylism very often accompanies acephalic conditions, and 

 other abnormalities due to defect of some organ, as recorded by 

 Fackenheim and others. Here the same law is applicable ; on account 

 of the abnormal absence of certain organic fundaments, the remaining 

 ones receive more than their usual amount of nutrition ; as a result, an 

 increased development of normally reduced or otherwise modified digits 

 may be brought about. But these cases of polydactylism may also bo 

 explained as due to external influences acting in utero. Fackenlieim has 

 shown that in a certain family polydactylism did not appear as a correla- 

 tive of inherited abnormality by defect, until one of its members married 

 into another family in which digital' abnormalities were of frequent occur- 

 rence. Then only did offspring appear afflicted with both polydactylism 

 and defective teeth. From such cases the evidence that excess of nutri- 

 ment causes germinal variation loses much of its weight. 



Any explanation of the phenomena of germinal variation must neces- 

 sarily be theoretical, as long as our practical knowledge of the germ-plasm 

 is so limited. We know, however, that all neomorphs are prone to varia- 

 tion. In polydactylism all the digital abnormalities produced by internal 

 causes vary greatly, and the tendency to variation is inherited. By 

 Mendel's law tlie inheritance of these variations is explained, and the 

 puzzling point whicli Wilson ('96) attempted to clear up by his theory of 

 nutritive variation, is made plain, — the fact that in man an individual 

 having a polydactyle man us may produce offspring with abnormal pes or 

 Avith all extremities abnormal. In this case we may assume that the 

 variation first appeared on all extremities as. a duplication of the mini- 

 mus, due to the doubling of the determinants of these digits. On 

 marrying with a normal individual the abnormal character would be 

 dominant, but not completely so (Bateson found this to be the case with 

 the polydactyle fowl). Of the DR offspring produced, some would be 

 abnormal like the D parent, but in others the usually dominant character 

 might be recessive ; their extremities might be entirely normal, or only 



