Eeactions and Products in Interspecific Crosses 



157 



thorax coloration {D), and others that breed true, and also combinations that 

 are hybrid and not shown. The point of interest is the showing that a form- 

 determining agent is present, acting, and capable of change, and the interchange 

 of the pattern systems of the pronotum. 



Fig. 11. 



The existence of the form-determiner is shown by the derivation from the Fg 

 array of decemlineata forms that are approximately the result of the combina- 

 tion of the basal form-factor of the tested race and the form-determiner from 

 the melanothorax type, which result could only be produced in this test by the 

 transfer of the form-determiner from the melanothorax type to the tested type, 

 and the result is precisely that which is expected. 



This test is in all respects a routine Mendelian reaction, uninteresting, except- 

 ing in the ability which it gives to test the nature of the agents that are being 



