outcome of his mental bias and not of the logic of things. If he had
first enquired into the Wasp's habits, he would not have brought
forward as a serious argument an incident which had no connection with
the important question of animal reason.

I have reverted to this case to show the difficulties that beset the
man who confines himself to casual observations, however carefully
carried out. One should never rely upon a lucky chance, which may not
occur again. We must multiply our observations, check them one with
the other; we must create incidents, looking into preceding ones,
finding out succeeding ones and working out the relation between them
all: then and not till then, with extreme caution, are we entitled to
express a few views worthy of credence. Nowhere do I find data
collected under such conditions; for which reason, however much I
might wish it, it is impossible for me to bring the evidence of others
in support of the few conclusions which I myself have formed.

My Mason-bees, with their nests hanging on the walls of the arch which
I have mentioned, lent themselves to continuous experiment better than
any other Hymenopteron. I had them there, at my house, under my eyes,
at all hours of the day, as long as I wished. I was free to follow
their actions in full detail and to carry out successfully any
experiment, however long. Moreover, their numbers allowed me to repeat
my attempts until I was perfectly convinced. The Mason-bees,
therefore, shall supply me with the materials for this chapter also.

A few words, before I begin, about the works. The Mason-bee of the
Sheds utilizes, first of all, the old galleries of the clay nest, a
part of which she good-naturedly abandons to two Osmiae, her free
tenants: the Three-horned Osmia and Latreille's Osmia. These old