To give them free passage and allow them to penetrate to a distance one condition is indispensable: the enclosure in which the captive is confined must not be hermetically sealed; there must be a communication between it and the outer air.

This again points to the probability of an odour, although this is contradicted by my experiment with the naphthaline.
My cocoons were all hatched, and the problem was still obscure.

Should I begin all over again in the fourth year?
I did not do so, for the reason that it is difficult to observe a nocturnal butterfly if one wishes to follow it in all its intimate actions.

The lover needs no light to attain his ends; but my imperfect human vision cannot penetrate the darkness.

I should require a candle at least, and a candle would be constantly extinguished by the revolving swarm.