iz EXPERIMENTS WITH DROSOPHILA AMPELOPHILA. 
ancestry as the abnormal strain, and about one-third of 1 per cent of 
wild Drosophila ampelophila were found to be abnormal. For four 
generations after branching from the abnormal strain (five, counting 
mating 405) not a single abnormal individual was found, but in the next 
generation 1 fly out of 216 (0.5 per cent) had a very slight abnormality. 
In succeeding generations the percentage increased for a time, in spite 
of artificial selection to the contrary, and then diminished to zero under 
the same treatment. The abnormalities were all small, never greater 
than ‘‘medium.’’ Table 6 summarizes the history of this strain for 40 
generations. 
TABLE 6.—Fluctuation in percentage of abnormal individuals in a normal strain. 
Generations No. of No. of | Percentage || Generations No of No. of Percentage 
Geers No.of | bnormal.| a trAT, aS normal. | abnormal. Behe ot 
land2; 418 | 0 0.0 23 and 24 | 144 0 0.0 
3 4} 235 | 0 0.0 25 26, 239 0 0.0 
5 6 | > 675 | 1 0.2 27 28 | 257 1 0.4 
7 8 594 | 7 1.2 29 30°; "116 0 0.0 
9 10 336 31 8.4 || 31 32 195 0 0.0 
11 12 471 45 Set. i ise 34; 217 0 0.0 
13 14 0 YESS 14 7.1 || 35 36 148 0 0.0 
15 16 | 79 2 2.5 || 37 38 | 55 | 0 0.0 
1 18 110 5 4.3 | 39 40 | 63 | 0 0.0 
19 20 234 | 14 5.6 | | — 
21 22 56 2 3.4 | Total | 4,725 | 122 2.5 
It is to be noted that the percentage of abnormal individuals is greater 
in this strain artificially selected for normal venation than it is in nature. 
At first thought one would say that this is an effect of the environment 
to which they were subjected. If this be true, environment may have 
played a part in the production of the abnormal strains. I think, how- 
ever, that itis not true. A sufficient explanation seems to lie in the 
fact that a form of selection exists in nature which is keener than the 
artificial sort, even when the latter is carried out under a lens. 
THE EEFECT OF SELECTION. 
Of late years there has arisen considerable skepticism concerning the 
cumulative effect of selection except as a means of isolating ‘‘ pure 
lines.’”’ Jennings (1908) says: ‘“‘ Certainly, therefore, until some one 
can show that selection is effective within pure lines, it is only a state- 
ment of fact to say that all experimental evidence is against this.’’ 
Whether or not the present material has a bearing upon the question 
thus clearly put depends upon the definition of a pure line. Ifa pure 
line be defined as one from which nothing else can be gotten by selec- 
tion, further discussion is not necessary. On the other hand, if inbreed- 
ing (for the most part, brother x sister) for 10 or 15 generations and 
rigid selection (in this case, with respect to wing-venation) may be 
