8 



AN ANALYSIS OF THE EFFECT OF SELECTION. 



hours (usually about 24 hours). Paper toweling was added to absorb 

 surplus moisture. 



The experiments were begun in New York City in February 1916, 

 and were carried on there until the middle of June, when the material 

 was moved to Woods Hole, Massachusetts, and continued there until 

 the end of September. All these flies were kept at room temperature. 

 The work was resumed in November, in New York, and continued 

 until the middle of May 1917. During these last six months the 

 flies were reared in a heated case that was regulated by a thermostat, 

 so that the minimum temperature was about 24, the maximum being 

 about 26, except when room temperature went a few degrees higher, 

 as occasionally happened. It is to be noted that the constant-tempera- 

 ture series run more evenly (see especially 1002 line), thus suggesting 

 that temperature influences bristle number. 



In order that the data presented in the Appendix may be correlated 

 with this information, if it seems desirable to do so, the following 

 table is presented. Each culture received a serial number at the time 

 the parents were mated, and these numbers run consecutively through- 

 out all the author's recent experiments (on other problems as well as 

 selection). These serial numbers are recorded in the Appendix. 

 Therefore, it is possible to fix approximately the date on which a cul- 

 ture was made up, if we know the date on which a culture with a simi- 

 lar number was made up. The dates of all cultures are noted on the 

 record sheets, but it has seemed hardly necessary to present more than 

 the following "landmarks." 



TABLE 6. 



SELECTION. 



If the variations observed in the Dichaet character are due to modi- 

 fication of the Dichaet gene itself, selection should be as effective in 

 inbred stocks as in any other kinds. If multiple factors are responsible 

 for the variations, the method of breeding should affect the result. 

 If a stock is closely inbred while being selected, it will soon become 

 fairly uniform, so that selection should be effective for only a com- 

 paratively short time. But if a strain is subjected to some crossing 

 it will become uniform more slowly, so that selection should be effective 



