In the old days, the Mason-bees used to surprise me greatly with their tenacious memory of the spot where the pebble lay supporting their nest and with their lack of perspicacity in all that concerned the nest itself, which was replaced by another, quite different nest without making them interrupt the work already begun. The Pelopæus outdoes them in these aberrations: she gives the last strokes of the trowel to an imaginary dwelling, of which nothing but the site remains. Has she, as a matter of fact, a more obtuse intellect than the dome-builder? The entomological tribe seems hardly to swerve from a common stock of aptitudes; those whom we consider the most richly endowed, on the evidence of actions normally accomplished, show themselves as limited as the rest when the experimenter disturbs the current of their instincts. It is probable that the Mason-bee would have committed the same absurdities as the Pelopæus, had I thought of subjecting her, at a propitious time, to a similar test. A plasterer by profession, she would, like the other, have plastered the base of the nest removed from the pebble at the right moment. My confidence in the glimmer of reason which the makers of theories attribute to the animal is so greatly shaken that I do not regard my unflattering opinion of the Mason-bee as rash. Thirty times, I said, in my presence did the artist in earthenware lay and then spread her pellet of mud upon the bare wall, thinking that she was applying it to the nest itself. Sufficiently informed by this long perseverance, I left the Pelopæus still busy at her futile task. Two days later, I inspected the plastered site. The coating of mud did not differ from that shown by a finished nest. I have suggested that the insect’s rudimentary intelligence has practically the same limitations everywhere. The accidental difficulty which one insect is powerless to overcome, in default of a gleam of judgment, any other, no matter what its genus or species, will be equally unable to overcome. To vary the evidence, I will borrow my next example from the Lepidoptera. [45]