The Heteropoda are further remarkable for the high development of their cephalic eyes, and for the typical character of their osphradium (Spengel's olfactory organ).
It will be remembered that, according to Spengel, the osphradium of mollusca is definitely and intimately related to the gill-plume or ctenidium, being always placed near the base of that organ; further, Spengel has shown that the nerve-supply of this olfactory organ is always derived from the visceral loop. Accord ingly, the nerve-supply FIG.
To the right of Spengel's osphradium is the opening of a peculiar gland which has, when dissected out, the form of a bunch of grapes; its secretion is said to be poisonous.
On account of the shortness of the visceral loop and the proximity of the right visceral ganglion to the oesophageal nerve-ring, the nerve to the osphradium and olfactory ganglion is very long.
In aquatic Pulmonata the osphradium is retained.
Near to each rudimentary ctenidium Spengel has discovered an olfactory patch or osphradium (consisting of modified epithelium) and an olfactory nerve-ganglion (fig.
Shell inrolled, solid, polished, aperture very narrow in adult; short siphon; anus posterior; osphradium with three lobes; mantle reflected over shell.
Spengel's observation of the osphradium and its nervesupply in these forms; the nerve to that organ, which is placed somewhat anteriorly - on the dorsal surface - being given off from the hinder part (visceral) of the right compound ganglion - the fellow to that marked A in fig.
In front of the osphradium is the single genital pore, the aperture of the common or hermaphrodite duct.
Instead of being destral, 'the osphradium is on the left side, and receives its nerve from the left visceral ganglion, the whole series of unilateral organs being reversed.