120 



General Discussion. 



Tlie following is oU'erecl by way of explanation of the foregoing facts. 

 Let it be assumed that the complex upon which the length of life of the 

 wild fly depends is expressed by the formula AB. The Truncate stock 

 arose as a mutation from the wild stock and possibly some factor has 

 changed to a. Consequently its formula would be aB. The inbred stock 

 had been In captivity for some time, and it is possible that the B had 

 (hanged to b. Its formula would l)e Ab. On crossing these two stocks a 

 hylii-id would result, the formula for which is abAB. Consequently in the 

 hybrid, normal conditions ai-e restored, and a fly results that lives longer 

 than either parent. The same explanation hohls in the case of the 

 increased egg i)r()duction to be seen in the hylnid. If this is true we 

 should expect to find wild stocks that live aliout fifty days and with high 

 egg producti«m and high fertilizing ]>ower of the gametes comljined. They 

 should be very higli producers. The nunilier of f;ictors, however, is nut 

 looked u])on to be as simple as the formula woviid seem to indicate. In- 

 stc.id of two factors as the formula shows, there may I)e many hundreds, 

 but the principle is the same. The things lost or changed in the germ 

 plasm of one stock are compensated in the liyl)ri(I liy the factors trans- 

 mitted by the othei' stock, and thus noi'uial conditions are restored. 



6. CONCLISIONS. 



1. Hybrids iietween the Truncate stock and the Inbred stock are 

 more vigorous than either parent as shown I)y the fact that the hybrid 

 lives 47 days while the parents live 21.4 and ;J7.4 days respectively. 



2. The flies from the Ti-uncate stock live 21.4 days. The females 

 live 18.4 while the males live 2G.4 days. 



3. The flies from the Inbred stock live .■)7.4 days. The females live 

 '.'A.it days while the males live 40.5 days. 



A. The shortened length of life of the Truncate stock reappears 

 among the grandchildren after skipiiing a generation when crossed to 

 the Inbred stock. The grandchildren lived an average of 29.5 days. 

 Tho.se descended from the Truncate grandmother lived 29.5 days. The 

 males lived 32.8 days and the females lived 25.9 days. The flies de- 

 scended from tbe Truncate .grandfather lived 29.:? days. The males lived 

 31.1 days, wliilc the females lived 27.3 day.s. 



