254 PHYSIOLOGICAL GENETICS 



(at 18°C). In the first, a temperature shock enlarges the sym- 

 metry field; the operation shows that the determination is not 

 yet finished and that the stream is in progress. In the second 

 half of the 3-day period, temperature shock produces narrowing 

 of the field in question. The operations (destruction of parts of 

 the field) produce the same effect and show in 48 to 60 hr. old 

 pupae the determination stream in flow, as reported. It starts 

 from both wing margins, joins in the center and then spreads 

 toward wing base and tip. A stopping of this flow means a 

 smaller field. One of the mutant genes Sy stops this process of 

 spreading before it is finished. Certain steps of this spreading 

 process are more frequently realized in the different experiments, 

 which might indicate areas of special resistance to the spreading 

 (or a wavelike process of spreading, Goldschmidt); one such 

 line coincides with the limits of the fields produced by the gene Sy. 

 There is another gene Syb, which broadens the field of symmetry; 

 this might also be done by temperature shock. The two effects 

 cannot be added (see the different behavior of the vestigial case, 

 page 22), and therefore the authors assume a line of absolute 

 resistance in the substratum. Here, then, have been analyzed 

 two phases that might influence the pattern by quantitative 

 variations and their mutual interplay: (1) what the authors call 

 the impetus of spreading, which is the same as the quantity of 

 determining substance in Goldschmidt's old interpretation; (2) 

 the resistance to spreading, which in Goldschmidt's terminology 

 was the conditions of the system. Since it is found that opera- 

 tions upon AS?/-animals more frequently fit one definite stage of 

 the spreading of the determination stream, as compared with the 

 same operations upon Wild type, it is specifically concluded that 

 the gene Sy does not affect the stream but the resistance of the 

 substratum, preferably at a definite time. These and similar 

 facts then demonstrate clearly the presence of a system of such a 

 type as had been postulated by Goldschmidt in his first attacks 

 upon the problem. 



• As all these details are rather complicated, we might finally give 

 a short picture of the origin of any more complicated type of wing 

 pattern, adding that each of the steps may be controlled by 

 mutant genes, which shift the process in question quantitatively 

 in time of onset, duration of action, locus of action, quantity 

 of reaction product, and threshold of action. The first pattern 



