10 EXPERIMENTS WITH DROSOPHILA AMPELOPHILA. 
vertical. The close fit of this line to the observed data shows that the 
relation 
Percentage of abnormal females —1.5 X percentage of abnormal males 
may be taken as approximately describing the average observed con- 
dition. 
Owing to the impossibility of describing the intensity of abnormality 
in quantitative grades, we can not give a formula for showing its sexual 
relation. Tables 2 and 3 show that there is sucha relation. The ques- 
tion as to whether both wings or only one shall be abnormal is also a 
part of this same problem of the variation of the intensity of the abnor- 
mality. We have seen that when a female is abnormal she will in 74 
per cent of the cases be so abnormal that both wings will be affected, 
while only 62 per cent of her abnormal brothers will be abnormal in both 
wings. 
THE RANGE OF VARIATION OF ABNORMALITY INCLUDES ‘‘NORMAL’’ VENATION. 
One other point is to be noted. The intensity of abnormality ranges 
all the way from cases in which there is almost as much abnormal vena- 
tion as normal down to a barely discernible devia- 
tion from normality. We have, then, in studying Srnec 
the inheritance of abnormal venation, the serious —_|abnormatfiies| C.S. | 
difficulty that a just indiscernible abnormality may =—§-_P®? "lv: 
be present.* Such a fly would be recorded as nor- 1to 20... 20.9 
mal. Table5 suggests that they would be more like- 2 = De 20.9 
ly to occur in families in which the percentage of _| 61 to 80...| 58.0 
abnormal offspring is low, for as such percentage | 81 to 100...) 83.1 
decreases the percentage of abnormal individuals 
which are abnormal on both sides (C. S.) decreases. In other words, 
there is an increasing percentage of abnormal flies which have the abnor- 
mality so reduced that in at least one wing it can not be seen. Hence, 
presumably, there is an increasing percentage of flies which have the 
abnormality reduced in both wings to a point just below visibility. 
These will be more common among males than among females, because 
the intensity of the abnormality is less in male than in female wings. 
Whether this alone accounts for the fact that a smaller percentage of 
brothers are visibly abnormal than of sisters isa question to which it is 
difficult to give an answer. 
*May not this be true also of the spotted condition in certain mammals? A guinea- 
pig still behaves as a spotted animal even if the spots are reduced until only the eyes 
remain affected. If the variation goes still further we would have an animal germi- 
pally spotted, somatically spotless. We would then say that the spotted condition is 
‘‘latent.”’ \ 
