Modification of Germinal Constitution of Organisms 213 



of the chapter. Morgan, in Drosophila ampelophila Low, 

 found that sex-limited variations of pink eye, etc., have 

 apparently followed the treatment of cultures of this animal 

 to the action of radium bromide. Loeb, however, using the 

 same organism, found that in both experiment and control 

 the variation described by Morgan appeared, and of course 

 concluded that the tendency to produce this variation was 

 already present in the race of flies used. 



Lutz had for several years used the same strain of 

 Drosophila for experiment, and found much variation in wing 

 venation. He also subjected the strain at times to different 

 experimental conditions, and this may be responsible for the 

 appearance of the variation found by Morgan following the 

 use of radium, and which appeared in experiment and control 

 in Loeb's experiments. 



In Chrysomelid Beetles 



In the modification of the germinal constitution by 

 experimental means it must be known as certainly as is 

 possible whether there are in the germ potential capacities, 

 i.e., latent characters, which ordinarily are not visible in 

 the materials used, but which may be called into visibility, 

 periodically or rarely, by unusual conditions. Unless pos- 

 sibilities of this kind are eliminated, it becomes difficult 

 in experiment to decide whether observed results are the 

 product of latent conditions, or of the experiment as de novo 

 variations. Moreover, experiments to show the effect 

 of incident conditions upon the germinal material must, 

 beyond any question, show that the effect is primarily 

 upon the germ and not first upon the soma of the parent, 

 and secondarily, by transmission, to the germ. If, in 

 experiment, the soma of the parent and of the resulting 



