136 NATURAL INHERITANCE. [CHAP. 



the influence, pure and simple, of the Mid-Parent may 

 be taken as ^, and that of the Mid-Grand-Parent as ^, 

 and so on. Consequently the influence of the individual 

 Parent would be 5, and of the individual Grand-Parent 

 ^$, and so on. It would, however, be hazardous on the 

 present slender basis, to extend this sequence with con- 

 fidence to more distant generations. 



Pedigree Moths. I am endeavouring at this moment 

 to obtain data that will enable me to go further, by breed- 

 ing 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 chloro- 

 form 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 con- 

 ditions, 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 



