180 Trans, Acad. Sci. of St. Louis 
season, and has three or four cells to each nest. By the 
third week in July, the population was noticeably wan- 
ing, and before the end of the month had almost dis- 
appeared. 
When these bees make their turrets, they use a process 
which I have not yet been able fully to analyze. The 
bee walks out backward, and when the tip of the abdo- 
men touches the rim of the chimney, she applies her 
pellet of mud. At first this is quite crumbly, but soon 
one sees that in some way water passes over it, making 
it more plastic and adhesive. One can see the water as 
it spreads over the mud, but cannot see where it comes 
from. It does not seem to come from out of the ab- 
domen and if it comes from the mouth one cannot see 
how it is passed to the tip of the abdomen. One load of 
mud brought from within makes from one-fourth to one- 
third of a ring. 
‘As mentioned before, the only perceptible differences 
between the chimneys of these bees and those of A. 
abrupta, are that these turn upward instead of project- 
ing from the bank horizontally, and these are usually 
solid tubes while those of A. abrupta have a gap or fis- 
sure, of unknown significance, extending the full length 
of the tube on its upper side.* Sometimes this upward 
turning chimney goes into pretty curves, but it never 
fails to turn upward. This distinction is unusually short 
and clear for the two species; I have never yet seen an 
A. abrupta go into one of these vertical turrets, nor 
have I ever seen an A. raui enter the horizontal ones, 
although I have often seen both species go into holes 
that had no turrets. 
*Out of several hundred turrets of A. ebrupta, only twelve lacked 
this split. 
