8 The Philippine Journal of Science 1922 
cases had occurred. But the deformity of the grandparent was 
never identical to that of the grandchild, which fact again speaks 
‘ against the theory of atavism. 
Finally, the theory falls short if we remember that in these 
deformities there is great variation in details; no two deformed 
extremities in the same individual or in any two individuals are 
found exactly identical, and certainly we agree with Gegenbaur, 
that it is inconceivable that one extremity has one atavus while 
the other has another. 
Heredity.—Heredity is, in our opinion, a more plausible theory 
than any of those given above. It explains not only most of the 
conditions, such as marked tendency to symmetry and quadru- 
plicity, found in these and allied deformities, but also the occur- 
rence in families through several generations. 
The occurrence of these deformities in reported single cases, 
like ours for instance, is not sufficient to overthrow the theory ; 
for in such cases the deformities might have been screened by the 
families, or these single cases might have been the first to occur 
in a family some of the descendants of which would be deformed. 
The following table shows the strong hereditary tendency of 
this deformity as well as its allied deformities, brachydactyly and 
polydactyly. The numbers given in the columns under the dif- 
ferent authors mentioned in the title indicate the deformed 
members in each generation in several families of these family 
trees, discussed by the authors. It does not include normal 
families in the same family trees. 
The scheme of the transmission of deformity, however, is hard 
to define. It may be that the deformity determinants are trans- 
mitted through the gametes; but, are all gametes carriers of 
these determinants? Apparently this was not so in the twins of 
Mayer’s family, one of which was deformed while the other was 
normal; nor in the families of Wilson and of Hasselwander where 
the deformity escaped one generation in some cases. But this 
discontinuity may still be explained by conceiving the deformity 
as made latent in one or two generations by the intervention of 
other characteristics. 
It is, nevertheless, inconceivable that these determinants are 
invariably transmitted in some fixed form, for it has been shown 
that no two extremities or individuals had exactly identical 
deformities; and, as Lewis and Embleton say— 
It seems far more probable that a fundamental factor, which influences 
the ultimate general confirmation of the affected parts thru their normal 
representatives, is at fault, that it is transmitted, and that its interaction 
