118 Experimental Zoology 
If polydactylism is dominant and the normal condition is reces- 
sive, the chances are that any polydactyi person has had one nor- 
mal parent and the germ-cells are therefore P and N.’ Paired 
with a normal individual (N + N), half the children should be 
polydactyl and half normal. In the above case there were in 
fact in the first generation four normal and four polydactyl chil- 
dren. In the second generation when normal offspring paired 
with normal, 5 polydactyl children and 21 normal were pro- 
duced; and when the polydactyl descendants paired with nor- 
mal, 7 polydactyl children and 12 normal were produced. 
For the small number recorded, the latter result is not very 
different from 1:1, the Mendelian ratio. Again in the third 
generation when P was mated to N, 5 normal and 5 polydactyl 
children were born. 
Struthers gives the following case of polydactyl inheritance in 
man : — 
I. Px ? 
1 P(xN) 1oP 
II. 
3P. rt P(xN) 
II. 4N 4P 
The result can only be explained on the Mendelian view byassum- 
ing that both parents of the first generation were polydactyls, 7.e. 
produced germ-celis bearing polydactylism. It is necessary to 
make this assumption in order to account for the second genera- 
tion that descended from one of the first filial generation. Here 
a polydactyl parent married a normal individual and produced 
only polydactyl children, showing that no normal germ-cells 
were present in one parent. Had there been some normal germ- 
cells, some normal children would be expected, provided the 
numbers are really large enough to give this result a chance to 
appear. In the third generation an equal number of the two kinds 
of offspring are expected, and such are found. A third case is 
1 Or P(N) and N(P) on my view. 
