464 Trans. Acad. Sci. of St. Louis 
wise in those cases wherein she accepted the proffered 
aid she did so with such outward indifference, taking it 
all as a matter of course after the manner of those ac- 
customed to welcoming charity, that I could not discern 
whether or not she was the wiser. 
In recent years the phrase ‘‘chain instincts’’ has fig- 
ured largely in the literature of comparative psychol- 
ogy. Very probably some creatures are guided largely 
by so-called chain instincts, and in reading some of the 
details in the foregoing pages some may say that this 
is true of S. caementarium also. Bouvier says in speak- 
ing of the mason bee: ‘‘If she is engaged in building, 
one can give her in exchange an entirely completed cell 
filled with food but she will keep on building and adding 
‘material to the already completed cell. If she is in the 
act of collecting food, she does not try to finish an in- 
complete cell which has been given her, but seeks rather 
a strange cell in the proper condition in which to store 
her honey.’’ 
It is altogether likely that these creatures are in a 
considerable degree guided in their sequence of activi- 
ties by ‘‘chain instincts,’’ that type of behavior upon 
which Fabre bases such sweeping generalities already 
quoted. I cannot believe, however, that in this group 
of organisms it is the omnipotent guide that some would 
have us believe. Individual temperament and a gleam 
of something more plastic than stubborn instinct some- 
times enter in to cause some surprising variations in 
their conduct; it is a satisfaction to find that in some 
individuals, perhaps a little more highly endowed, the 
chain may actually be broken or even reversed. 
For instance, in Exp. XI a wasp returning with mud 
to seal a cell and finding it had been broken into, so far 
forgot the usual sequence of activity or escaped its im- 
