Pee W. J. MOENKHAUS 
first five or six generations. As previously stated, up to this time 
the method consisted in placing pairs of brothers and sisters in 
each of five vials to insure against mishaps. These mishaps con- 
sisted of drying up of the food, attacks of fungus and in some cases 
the escape of the flies themselves during the process of feeding ete. 
Those pairs that produced young were regarded as having es- 
caped these various possible mishaps and were taken as indica- 
tions of the vitality and productiveness of the strain. Theexpecta- 
tion at that time was that any deleterious effect of the inbreeding 
would show itself in the offspring of any of the pairs. Conse- 
quently, when a given pair would produce offspring that was num- 
erous, all well formed, vigorous, and in no apparent way differing 
from normal offspring, to see whether some slight influence might 
not be present that could not be detected by ordinary observation a 
definite measure was taken of (1) their rate of reaction to light and 
gravity, (2) the total number of eggs produced and (3) the percen- 
tage of eggs which hatched and emerged. An attempt was made to 
determine their length of life but this proved too prolonged to 
allow one to carry it out together with all the other incidents of 
the already too laborious experiments. 
The reaction of this animal toward light and against gravity 
is well known. To get a measure of the rate of reaction the ani- 
mals were made to travel through a glass tube that had been 
blackened for 16 cm. on the inside. This tube had a light placed 
at one end and was inclined about twenty-five degrees. From a 
glass vial the flies were admitted, one at a time, into the tube and 
the time from the moment of entrance into the blackened portion 
of the tube to their emergence was recorded. It was found essen- 
tial that the two batches of flies (inbreds and normals) should be of 
the same age, be reared under the same conditions and that the 
temperature of the room be the same for the two batches. The 
results are as follows: at a temperatureof 27.2° C. 133 normals 
took 16 seconds, average, to travel the distance, and 140 inbreds 
took 15.4 seconds. The two sexes in these two groups were about 
equal in number. In both groups the males travel the distance 
on an average in three seconds less time. It is clear from this 
that the normals and inbreeds are equally responsive to these two 
