244 Trans. Acad. Sci. of St. Louis 
vertical position (Fig. 20E) most of them were hort- 
zontally resting on top of the bank, near the edge (Fig. 
21E). All of the nests of this species enjoyed an abun- 
dance of the sunlight; those on top of the bank were 
made very near to the front edge. However, during 
the years that followed this species decreased in num- 
bers so that by 1920 it was barely holding its own, 
whereas A. abrupta increased amazingly, as described 
elsewhere. Another interesting factor enters into the 
story here, however; during the years under observa- 
tion the white-banded bees gradually extended their nest- 
ing area. In 1917 most of them were in among the An- 
thophora nests near the sunlight, either in the face of 
the bank or near the edge of the top (Figs. 20E and 21K) 
with merely the beginning of a settlement at the extreme 
south end and another at the north end. In 1918, they 
were almost all in these two end groups, and none among 
the Anthophora nests. In 1919 a few were at the south 
end, but most of them were on the top, farther back than 
previously, and in 1920 to 1922, all of the burrows found 
were far back on the bank and entirely out of the direct 
sunlight. In the meantime Anthophora abrupta was in- 
creasing in numbers, always building on the sunny face 
of the bank. Moreover they were gradually spreading 
over the southern portion of the bank, until by the end 
of the period the north half of the dark barren portion 
seen in Fig. 3 was abundantly inhabited; Fig. 22 is 
the same area as in Fig. 3. Not without cause, however; 
was this significant change; in the spring of 1918 the 
tenants of the house had cut the ramblers almost to the 
ground, so for the seasons immediately succeeding, that 
portion of the bank was also fully exposed to the 
sunlight. 
