In a large genus it is probable that more than one species would vary.

In the diagram I have assumed that a second species (I) has produced, by analogous steps, after ten thousand generations, either two well-marked varieties (w10 and z10) or two species, according to the amount of change supposed to be represented between the horizontal lines.

After fourteen thousand generations, six new species, marked by the letters n14 to z14, are supposed to have been produced.