This breaking up, on the one hand, into sections in all of which both sexes are represented and the division, on the other hand, of the entire laying into just two groups, one female, the other male, when the length of the tube permits, surely provide us with ample evidence of the insect's power to regulate the sex of the egg according to the exigencies of space.
And besides the exigencies of space one might perhaps venture to add those connected with the earlier development of the males.

These burst their cocoons a couple of weeks or more before the females; they are the first who hasten to the sweets of the almond-tree.

In order to release themselves and emerge into the glad sunlight without disturbing the string of cocoons wherein their sisters are still sleeping, they must occupy the upper end of the row; and this, no doubt, is the reason that makes the Osmia end each of her broken layings with males.

Being next to the door, these impatient ones will leave the home without upsetting the shells that are slower in hatching.
I had offered at the same time to the Osmiae in my study some old nests of the Mason-bee of the Shrubs, which are clay spheroids with cylindrical cavities in them.

These cavities are formed, as in the old nests of the Mason-bee of the Pebbles, of the cell properly so-called and of the exit-way which the perfect insect cut through the outer coating at the time of its deliverance.