In Papilio turnus there exist, in the southern states, two kinds of females, one yellow like the male, one black (fig. 27). The evidence here is not so certain, but it seems probable that a single factor difference determines whether the female shall be yellow or black.
Finally in Papilio polytes of Ceylon and India three different types of females appear,
(fig. 28 to right) only one of which is like the male. Here the analysis of the breeding data shows the possibility of explaining this case as due to two pairs Mendelian factors which give in combination the three types of female.
Fig. 28. Papilio polytes, with three types of female to right and one type of male above to left.
Taking these cases together, they furnish a much simpler explanation than the one proposed by Darwin. They show also that characters like these shown by wild species may follow Mendel's law.
Fig. 29. Mutant race of fruit fly with intercalated duplicate mesothorax on dorsal side.
There has appeared in our cultures a fly in which the third division of the thorax with its appendages has changed into a segment like the second (fig. 29). It is smaller than the normal mesothorax and its wings are imperfectly developed, but the bristles on the upper surface may have the typical arrangement of the normal mesothorax. The mutant shows how great a change may result from a single factor difference.