I found them almost everywhere in the neighbourhood of their goal.

When the captive was in my study the butterflies did not all enter by the open window, the direct and easy way, the captive being only a few yards from the window.

Several penetrated the house downstairs, wandered through the hall, and reached the staircase, which was barred at the top by a closed door.
These data show us that the visitors to the wedding-feast did not go straight to their goal as they would have done were they attracted by any kind of luminous radiations, whether known or unknown to our physical science.

Something other than radiant energy warned them at a distance, led them to the neighbourhood of the precise spot, and left the final discovery to be made after a vague and hesitating search.

The senses of hearing and smell warn us very much in this way; they are not precise guides when we try to determine exactly the point of origin of a sound or smell.
What sense is it that informs this great butterfly of the whereabouts of his mate, and leads him wandering through the night?
What organ does this sense affect?
One suspects the antennae; in the male butterfly they actually seem to be sounding, interrogating empty space with their long feathery plumes.