the same; and the place of arrival, the distance, the time of day, all
remain unchanged. Of the five with whom I experiment, I find three at
their nests next day; the two others are missing.

It is therefore fully established that the Mason-bee of the Walls,
carried to a distance of two and a half miles and released at a place
which she has certainly never seen before, is able to return to the
nest. But why do first one out of two and then two out of five fail to
join their fellows? What one can do cannot another do? Is there a
difference in the faculty that guides them over unknown ground? Or is
it not rather a difference in flying-power? I remember that my Bees
did not all start off with the same vigour. Some were hardly out of my
fingers before they darted furiously into the air, where I at once
lost sight of them, whereas the others came dropping down a few yards
away from me, after a short flight. The latter, it seems certain, must
have suffered on the journey, perhaps from the heat concentrated in
the furnace of my box. Or I may have hurt the articulation of the
wings in marking them, an operation difficult to perform when you are
guarding against stings. These are maimed, feeble creatures, who will
linger in the sainfoin-fields close by, and not the powerful aviators
required by the journey.

The experiment must be tried again, taking count only of the Bees who
start off straight from between my fingers with a clean, vigorous
flight. The waverers, the laggards who stop almost at once on some
bush shall be left out of the reckoning. Moreover, I will do my best
to estimate the time taken in returning to the nest. For an experiment
of this kind, I need plenty of subjects, as the weak and the maimed,
of whom there may be many, are to be disregarded. The Mason-bee of the
Walls is unable to supply me with the requisite number: there are not