136 NATURAL INHERITANCE. [CHAP.
the influence, pure and simple, of the Mid-Parent may be taken as Q, and that of the Mid-Grand-Parent as I,' and so on. Consequently the influence of the individual Parent would be }, and of the individual Grand-Parent A, and sb on. It would, however, be hazardous on the. present slender basis, to extend this sequence with confidence to more distant generations.
Pedigree Moths.--I am endeavouring at this moment to obtain data that will enable me to go further, by breeding Pedigree Moths, thanks to the aid of Mr. Frederick Merrifield. The moths Selenia Illustraria and Illunaria are chosen for the purpose, partly on account of their being what is called double brooded ; that is to say, they pass normally through two generations in a single year, which is a great saving of time to the experimenter. They are hardy, prolific and variable, and are found to stand chloroform well, previously to being measured and then paired. Every member of each Fraternity is preserved along three lines of descent-one race of long-winged moths, one of medium-winged, and one of short-winged moths. The three parallel sets are reared under identical conditions, so that the medium series supplies a trustworthy relative base, from which to measure the increasing divergency of the others. No one can be sure of the success of any extensive breeding experiment, but this attempt has been well started and seems, to present no peculiar difficulty. Among other reasons for choosing moths for the purpose, is that they are born adults, not
changing in stature after they have emerged from the
chrysalis and shaken out their wings. Their families
