The preceding eleven paragraphs are substantially but not verbally identical with the statement of the argument in Mr.Wallace's "Darwinism," 1889.
Pages 179, 180, note 1.) 12.

Let us now consider the more difficult case of two allied species A, B, in the same area, half the individuals of each (As, Bs) being absolutely sterile, the other half (Af, Bf) being partially fertile: will As, Bs ultimately exterminate Af, Bf?
13.

To avoid complication, it must be granted, that between As and Bs no cross-unions take place, while between Af and Bf cross-unions are as frequent as direct unions, though much less fertile.

We must also leave out of consideration crosses between As and Af, Bs and Bf, with their various approaches to sterility, as I believe they will not affect the final result, although they will greatly complicate the problem.
14.

In the first generation there will result: 1st, The pure progeny of As and Bs; 2nd, The pure progeny of Af and of Bf; and 3rd, The hybrid progeny of Af, Bf.
15.