Eggs deposited in a cocoon after copulation.
It is in this and related families that the greatest diversity in the colour and form of the cocoon is found.
Under the microscope cocoon silk presents the appearance (fig.
Fabre has found that in the nests of some species of Osmia the young bee developed in the first-formed cell, if (as often happens) she emerges from her cocoon before the inmates of the later cells, will try to work her way round these or to bite a lateral hole through the bramble shoot; should she fail to do this, she will wait for the emergence of her sisters and not make her escape at the price of injury to them.
When fully grown, the maggot spins an oval silken cocoon within which it pupates (fig.
It yields a large compact cocoon (fig.
The young leave the cocoon as fully formed earthworms in which, however, the genitalia are not fully developed.
Out of a single cocoon emerge a varying number of young worms, the numbers being apparently characteristic of the species.
The second step in the evolution of spinning instincts was probably the making of a silken chamber for the reception of the cocoon itself and for the protection of the mother while guarding it and her newly-hatched young.
If the attack comes on a short time before maturity, the worms are able to spin a cocoon of a feeble character, but worms with this disease never change into chrysalides, but always die in the cocoon before transformation can take place.