CEA FABER Valle 
ATAVISM (continued). 
Supernumerary Digits, Limbs, and Mammary Glands.— 
Nothing illustrates so forcibly the necessity of critically 
examining suspected cases of atavism as those abnor- 
malities collectively known as Polydactyly. At the 
outset it may be stated,.contrary to the prevailing 
opinion, that supernumerary digits are very rarely 
atavistic. 
The various examples of extra fingers, toes, arms, and 
legs, described in the chapter on Dichotomy, serve to 
show that if all supernumerary parts are to be regarded 
as reversions we must find vertebrates provided with an 
unlimited number of toes, double hands and feet, and 
more than two pairs of limbs. 
No vertebrate animals other than fish and the /chthyo- 
sauril, possess on each limb more than five digits, 
therefore when the number of toes or fingers exceed on 
each limb this typical number, it must if we, with 
Darwin, regard the accessory digit as atavistic, be a 
reversion to an Ichthosaurian or a fish form. The 
distance is far too great, and in doing so we violate the 
rule that atavistic parts do not belong to forms pale- 
ontologically remote or systematically far distant. 
