352 Trans. Acad. Sci. of St. Louis 
exposed to view, not having the plug at the opening. 
All of this shows that ‘‘habit’’ has not yet bound this 
creature to her wheel, and it suggests that this species’ 
instinct is today in a very unstable condition and will 
bear watching for a solution of some of the most per- 
plexing problems of psychic evolution. 
The promising prospect of wresting from P. mellipes 
some of the secrets of her nest-building caused me to 
return to Wickes. But on this second visit, in Septem- 
ber, the outhouse that had previously been of interest 
proved void of P. mellipes. At 5:35, however, almost 
twilight, I found in a dark corner of another shed nearby 
a P. mellipes atop the nest of a mud-dauber. The nest 
was more or less dilapidated, with whole sides torn out 
of certain cells. At first this condition aroused little 
attention, since I thought the nest had merely met with 
some calamity such as an attack by birds, or disintegra- 
tion by the elements. Later investigations, however, 
showed that this destruction was the work of P. mellipes; 
hence I give briefly the condition of the nest when found. 
One cell that had been sealed empty had the entire top 
removed; a second upper cell had likewise had the top 
torn away, but this had been a sealed cell, and the pupal 
case of the Sceliphron was hanging over one wall, where 
evidently it had been pushed by P. mellipes as she was 
demolishing the cell and carrying the mud inside for 
her new cells. The two cells underneath were of special 
interest. One had the wall about the opening removed, 
forming a rather large circular aperture, twice the size 
of the original opening. This cell will hereafter be re- 
ferred to as ‘‘X.’? The mandible-marks were vividly 
etched about the periphery. The other under cell was 
the main item of interest, because the P. mellipes was 
at the time building her own cells therein of the mud 
