INHERITANCE OF ABNORMAL VENATION. 13 
reasonably supposed to have established as ‘‘ pure’’ a line as exists in a 
given case, the following facts may be of interest. 
The abnormalities obtained, both in the direction of veins added and 
of veins lacking, far surpass those found in nature in this or any other 
insect with whichI am familiar. Furthermore, they do not even remotely 
suggest the venation of any of this fly’s relatives. Something new has 
been produced. Inthe strain whose early history has just been described 
there was, at the start, no definite effort made to build up an abnormal 
race as quickly as possible. Later I tried to do this from wild material 
obtained from other localities. 
Starting with an abnormal male and a normal female from Boston and 
an abnormal male and female from Bloomsburg, Pennsylvania, I rigidly 
selected for additional veins. The record for each successive set of two 
generations was 8.8, 5.5, 11.5, 14.38, 30.3, 45.8, 85.9, and 100 per cent 
abnormal. Thereafter mass-breeding was practiced and the abnormal 
strain preserved for about a year by merely starting a fresh jar every 
couple of weeks with the most abnormal individuals found at that time. 
The abnormalities in this strain were of the same nature and extent 
as in the one started from the Long Island material. It would seem 
that this increase in the percentage of abnormal individuals up to 100 
per cent and the subsequent increase of the intensity of the abnormalities 
can not be due to the gradual weeding out of all units but the one or 
several desired, because one quickly gets things which one can safely 
say did not exist in the population with which we started, or, to be more 
exact, which we do not see. Some can probably imagine that the “‘units’’ 
for each successive grade of abnormality existed in the parents with 
which we started, but that they were held in check by an equal number 
of inhibiting “‘units”’ of corresponding powers, so that the result could 
be explained by saying that in the selection we cut out step by step suc- 
cessively stronger inhibiting units, thus allowing successively greater 
abnormality-producing units to manifest themselves. On any other 
hypothesis, it seems to me, we must admit the cumulative effect of 
selection upon a “‘unit,’’ 7. e., within a pure line. 
But, upon this hypothesis, how can we account for the occasional nor- 
mal flies? Why do not the inhibiting units stay cut out after we have 
once gotten rid of them so thoroughly that all the flies of several suc- 
cessive generations show strong added veins? Perhaps they do stay 
cut out and these occasional normals are merely fluctuating variations 
in the abnormal unit. If so, and if selection does not have a cumula- 
tive effect within a unit, it would be impossible to return to normality 
from a series of inbred generations of abnormality. But it is possible. 
Starting with a family which had one normal offspring in a total of 133 
(99.2 per cent abnormal) and selecting to reduce the extra veins, the 
percentage of abnormal offspring in successive generations was 81.8, 
66.2, 32.9, 12.5, 17.0, 0.0, 0.0, 0.0, and so on, as a typical normal strain. 
