292 THE THEORY OF THE GENE 



abdomens, and at the same time and under like conditions 

 we breed the late hatching flies with normal abdomens, we 

 obtain exactly the same kinds of flies in the next genera- 

 tion. The first to emerge are abnormal, the later ones 

 more normal. It has made no difference whether the abdo- 

 men of the parent was normal or abnormal, so far as the 

 germ-cells are concerned. 



If it be said that the effects might be too small to be 

 seen at first, then I may add that late-hatching flies have 

 been bred from for ten successive generations without 

 any observed difference in the results. 



Another example is equally convincing. There is a 

 mutant stock of Drosophila called eyeless (Fig. 30). The 

 eyes are smaller than the normal eye and very variable. 

 By selection, a uniform stock has been produced in which 

 most of the flies are without eyes, but, as each culture 

 gets older, more and more flies have eyes, and larger 

 ones. If, now, we breed from the late-hatched flies, the 

 offspring are the same as when eyeless flies are used. 



Here the presence of eyes in the older culture is a posi- 

 tive character and might be considered to furnish better 

 evidence than the abnormal abdomen, where the sym- 

 metry and pigmentation of the late hatching larvae is 

 less obviously a present character. The outcome is, how- 

 ever, the same in both cases. 



It is quite unnecessary to attempt to consider here the 

 numerous claimants that have appeared in the last few 

 years, who have furnished " proof," as they say, of the 

 inheritance of acquired characters. I choose only one 

 case, that is the most complete of its kind, since it gives 

 the numerical and quantitative data on which the conclu- 

 sions are based. I refer to the recent work of Diirken. The 

 experiment seems to have been carefully made and ap- 

 pears to Diirken to furnish proof of the inheritance of 

 acquired characters. 



