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. 
Culture. Date. Culture. Date. Culture. Date. 
884 Feb. 3, 1916 1507 June 7, 1916 2389 Sept. 16, 1916 
1006 Mar. 24, 1916 1617 June 23, 1916 2423 Nov. 18, 1916 
1100 Apr. 16, 1916 1830 July 14, 1916 2601 Jan. 13, 1917 
1150 Apr. 22, 1916 2000 Aug. 1, 1916 2950 Mar. 17, 1917 
1301 May 15, 1916 2250 Aug. 28, 1916 3078 Apr. 15, 1917 
1401 May 28, 1916 
SELECTION. 
If the variations observed in the Dichet character are due to modi- 
fication of the Dichet 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 
