T. Lewis and D. Embleton 
49 
which can only be allowed if it can be shown that characters acquired in utero 
may be transmitted, are discountenanced by the statement of Vrolik that a normal 
father may give rise to two similar sport offspring from two separate normal 
mothers. There is however no recorded example of this sort as far as split-foot 
is concerned, and the argument therefore rests upon analogy ; but it may be said 
that on the whole the evidence is in favour of the presence of potential deformity, 
such as split-foot, in those factors in the germ cell wJiicli eventually influence the 
conformation of the Jiands and feet. 
When the enormous waste of sexual cells from both male and female genitors 
in the process of procreation is considered it becomes extremely probable that a 
vast number of sperms and a large number of ova contain the necessary generating 
factors of the deformity ; for otherwise the unlikelihood of a malformation ever 
showing in the next generation would be overwhelmingly great. The hypothesis 
is much strengthened by the fact that more than one deformed child may arise 
from the same normal parents^' Jt must also be remembered that at least 30 
such sports have been reported as occurring. If the position is accepted it follows 
that when all sports are considered a large proportion of the human race have the 
potentiality for producing such defects in their offspring. Also it follows that, if a 
similar potential deformity exists in an abundance of cells developed from a single 
individual, we have to choose between the possibilities of the origin of the 
determining factor in a single common precursor of these cells, and the origin of 
similar defects in each germ cell separately. The former is obviously the more 
plausible*. It remains for us to further discuss the nature of the particular sport 
with which we are dealing, and in so doing shall prepare the way for the con- 
sideration of certain suggestions relating to sport characters, which have recently 
been prominent. It has already been pointed out that there are records of over 30 
instances of the origin of this same sportf, and that whenever it occurs it tends to 
vary, when opportunity is given it, in the different individuals of the families. An 
apparent example of a sport tending to multiple variations, and one which we are 
inclined to regard as parallel to hereditary split-foot, is the remarkable plant 
Oenothera Lamarkiana and its mutations, discovered by de Vries. In all cases 
where families of split-foot have been described the variations have occurred, but 
what is no less remarkable is that the same sport, arising on so many separate 
* In assigning the origin to precursors of the sperm cells or ova, the unusual and recently dis- 
covered types of nitosis in these cells are not forgotten. But at the same time we cannot commit our- 
selves to a theory of origin or transmission through the medium of any particular anatomical structure. 
It is for this reason that we have avoided the use of the word " determinant," as it is too closely 
associated with these theories. 
t In regard to this statement it is essential to point out that in a small proportion of the cases, 
there has been no mention of descent from healthy parentage ; the possibility of two or more of them 
belonging to the same family can consequently not be placed entirely out of court, though its improba- 
bility is great. Moreover it must be remembered that although in the families examined there is 
no instance in which the deformity skips a generation, yet the presence of deformity in collateral 
branches cannot be absolutely excluded. Our subsequent conclusions must therefore be read with due 
regard to these possibilities. 
Biometrika vi 7 
