The process carrying the otolith outer side of a or concretion hk, formed by endoderm cells, is tentacle, two enclosed by an upgrowth forming the " vesicle," nerves run round which is not yet quite closed in at the top. the base of the (After Hertwig.) tentacle to it.
A single otolith is present as in the veliger embryos of Opisthobranchia.
The mouth is shown by the line surrounding the otolith (OT) in the centre.
The mouth is ventral, the otolith dorsal.
In Nausithoe a single large otolith is found: Natural size.
Where the sac is completely closed it generally contains no solid particles, but in a few Macrura a single otolith secreted by the walls of the sac is present.