One of Fryer's experiments may be given here in illustration of the nature of the evidence upon which the above hypothesis depends.
Families were reared from the two wild H females of whom nothing was known either as to ancestry or husband. The first family contained 10 M and 7 H females. Hence the original wild mother was probably iiXx and had mated with a male of the constitution
Iixx. The family from the second wild H female contained 26 H and 7 M females; i.e. the ratio in which these two forms appeared was not far from 3:1. Hence the wild female was probably iiXx and her husband IiXx. If this were so some of the 26 ♂♂ should receive the X factor from both parents and consequently be IiXX in constitution. This was almost certainly so in the case of the single male in this brood tested by mating with an M female from the other brood. All of his 12 daughters were of the H form, as should have been the case had his constitution been IiXX. Supposing this to be so, all his offspring, of both sexes, must be heterozygous for X. Consequently any pair mated together should give both H and M females in the ratio of three of the former to one of the latter. In Mr Fryer's experiment two males and two females chosen at random were mated together. In the one case six H and one M female were produced, in the other ten H and two M females. As was expected both classes of female appeared, and the looked-for ratio of three H to one M was, in view of the smallness of the numbers, not departed from widely in either instance.
In the experiments selected as an illustration, the mimetic females happen to be all of the H form. In other experiments, however, both the H form and the A form occurred. As the result of his experiments Mr Fryer came to the conclusion that here again the difference is one of a single hereditary factor. All mimetic females contain the X factor, but the H
females contain in addition a factor which we may call Y. The function of the Y factor is to carry the change made by the X factor a step further, and to turn the A form of female into the H form. Y is a modifier of X, but unless X is present Y can produce no effect. All the different individuals which are to be found among P. polytes in Ceylon may be represented as follows:—
| ♂♂ | M♀♀ | A♀♀ | H♀♀ |
| IixxYY | iixxYY | — | — |
| IixxYy | iixxYy | — | — |
| Iixxyy | iixxyy | — | — |
| IiXxYY | — | — | iiXxYY |
| IiXxYy | — | — | iiXxYy |
| IiXxyy | — | iiXxyy | — |
| IiXXYY | — | — | iiXXYY |
| IiXXYy | — | — | iiXXYy |
| IiXXyy | — | iiXXyy | — |
In this way is offered a simple explanation in terms of three Mendelian factors which serves at once to explain the various results of the breeding experiments, and the fact that intermediates between the different forms of female are not found.
The only other experiments comparable with these on P. polytes are some made by Jacobsen on Papilio memnon in Java[[46]]. Here again there are three forms of female, one of which, laomedon, is something like the male, while the other two, agenor and achates, are quite distinct. Of these three achates, unlike the male and the other two females, is tailed, and resembles
the species Papilio coon which belongs to the same presumably distasteful group as P. aristolochiae. These experiments of Jacobsen's are not so complete as the series on P. polytes, but Professor de Meijere and Mr Fryer have both pointed out that they are capable of being interpreted on the same simple lines.