THE MUTATED GENE 



199 



The idea of gene action by means of a determination stream has 

 also occasionally been employed by Drosophila workers. Thus 

 Plunkett (1926) found that the bristle-destroying action of the 



Fig. 38. — Flour moth, a, diagram of the spread of the determination stream; 

 h I, individual right pupal wings; b-f, black race; g-l, wild race;/, /, controls. 

 Age at operation g below 6\ b below 24 fc c-e, h-k 24-72 A . (From Kuehn and 

 Henke, 1936, Abh. Ges. Wiss. Goettingen 15, Fig. 97.) 



achaete gene spread from the center of its action (a definite 

 bristle) equally in all directions. As he assumes that the decisive 

 agent is a catalyst, he thinks that this diffuses from its point of 

 origin in all directions, a process, then, that we might describe 



