There must be something more.

And I was right: that arrangement in series is only a tiny fraction of the reality, which is remarkable in a very different way.

This is what I am going to prove by experiment.
The succession first of females and then of males is not, in fact, invariable.

Thus, the Chalicodoma, whose nests serve for two or three generations, ALWAYS lays male eggs in the old male cells, which can be recognized by their lesser capacity, and female eggs in the old female cells of more spacious dimensions.
This presence of both sexes at a time, even when there are but two cells free, one spacious and the other small, proves in the plainest fashion that the regular distribution observed in the complete nests of recent production is here replaced by an irregular distribution, harmonizing with the number and holding-capacity of the chambers to be stocked.

The Mason-bee has before her, let me suppose, only five vacant cells: two larger and three smaller.