Eeactions and Products in Intekspboifio Ckossbs 



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. 



PIQ. 11. 



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

 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 



