O, o, Right and left olfactory ce.pl, The cerebro-pleural conganglia and osphradia re nective.
Two osphradia present but no hypobranchial glands nor operculum.
RHIPIDOGL0ssA.-Aspidobranchia with a palliovisceral anastomosis (dialyneurous); eye-vesicle closed, with crystalline lens; ctenidia, osphradia and hypobranchial glands paired or single.
A pair of pedal otocysts, and a pair of osphradia at the base of the gills, appear to be always present.
United with these ganglia on the outer sides are the osphradial ganglia, above which the epithelium is modified to form a pair of sense-organs, corresponding to the osphradia of other Molluscs.
The special sense-organs are a pair of eyes on the head, a pair of otocysts or statocysts, and a pair of osphradia which have already been mentioned.