308 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
transmitted in a recessive condition through many generations, is in strict 
accordance with Mendel’s law of heredity. 
7. Neogenetic and palingenetic forms of polydactylism are, like other 
new characters, extremely variable; as they are hereditary, we may con- 
clude that duplications of both functional and vestigial digits are due to 
variations in the gametes. 
8. The polydactyle abnormalities of man and the domestic animals 
may be classified as follows: 
I. Teratological polydactylism includes those cases of digital duplica- 
tion and malformation which are produced by external influences ; it occurs 
rarely in all animals, often in correlation with other monstrosities. 
II. Meogenetic polydactylism includes those digital variations, or 
sports, which are produced by some internal cause, presumably germinal 
variation. 
a. Duplication of unmodified functional digits occurs occasionally in 
all animals and is transmissible. 
b. Variation of modified but functional digits is the ordinary form 
of polydactylism in man, the cat, and the fowl (pes), and it also is 
transmissible. 
III. Palingenetic polydactylism includes those cases in which digital 
rudiments, or vestiges, develop into extra digits. 
a, The extra digits reproduce more or less completely the structure of 
the homologous functional digits of related fossil ancestors ; this condi- 
tion is found in the horse, ruminants, swine, and the pes of the dog. 
b. The extra digits arise as variations or duplications of rudiments, or 
vestiges ; they are neogenetic in so far as they do not reproduce ancestral 
conditions. Examples are the hallux and pollex having three phalanges 
and the various duplications of these digits found in the manus of swine 
and the pes of Carnivora. 
