These are expelled along with mucus by the sneezing of the host.
They appear to be the principal source of the mucus these animals secrete.
This causes the entire skin to become dry - as in the case of the local action above mentioned; and it arrests the secretion of saliva and mucus in the mouth and throat, causing these parts to become very dry and to feel very uncomfortable.
In Yoldia and Nucula proxima the ova are set free in the water and the test-larvae are free-swimming, but in Nucula delphinodonta the female forms a thin-walled egg-case of mucus attached to the posterior end of the shell and in communication with the pallial chamber; in this case the eggs develop and the test-larva is enclosed.
The secretion of mucus by the bronchi and trachea is greatly reduced and their muscular tissue is paralysed - a fact of which much use is made in practical medicine.