168 Trans. Acad. Sci. of St. Louis 
lucky turn out of this misfortune; instead of going some 
distance to the roadway puddle for their water, a dozen 
bees with their long tongues protruding were lapping 
up the drops of water from the vegetation nearby. 
Frequent visits showed the activity of the A. abrupta 
bees to be the same without change in numbers up to 
July 12. Thus the entire population lived practically 
simultaneously, without individual variation in time. 
During the four days from July 12 to 16, the number of 
workers dwindled alarmingly from day to day. This sud- 
den dropping off led me to believe that I was witnessing 
the death and the end of the first generation. I hoped 
that the second generation would come soon enough and 
be large enough to give me material for certain homing 
studies without the danger of exterminating them. The 
next few days saw the demise of the last few survivors; 
but my anticipation of a second generation was in error, 
for no others appeared that year. Furthermore, in the 
years following I found only one generation of these 
bees each year, and that with a remarkably short life 
eycle. In this 1917 brood, the duration of adult life was 
less than thirty days, the first bees emerging a few days 
before June 25, and the last ones dying about July 16. 
While daily visits during the following week proved 
that A. abrupta had entirely disappeared, these daily 
visits also made it conspicuously clear that another 
species of turret-building mining bee, Entechnia taurea, 
had emerged from the bank and was busily engaged in 
nest building activities. And in precisely the same way 
in the following years it was observed that just as soon 
as A. abrupta had finished her labors and gone the way 
of all flesh, then the white-banded bees appeared upon 
the scene. The interrelations of the two species of bees 
