=Position of Olfactory Organs in Pulmonata.=--Most authorities are of opinion that the olfactory organs are situated in the tentacles. Moquin-Tandon considered that in the Helicidae and Limacidae the sense of smell is confined to the little knob or elevation at the end of the longer tentacles, close to the eye. He found that when he cut off these tentacles both in _Limax_ and _Arion_, the creatures were quite unable to discover the whereabouts even of strongly-scented food. The same author believed that in the Basommatophora the sense of smell was present in the whole of the tentacle, which is covered with an exceedingly sensitive ciliated epithelium. Lacaze-Duthiers, however, places the olfactory sense in this group at the outer side of the base of the tentacles, near to the eyes. Some authorities[303] deny that the Helicidae have the olfactory organ at the tip of the tentacles, and locate it in a pedal gland near the mouth, which contains conspicuous sensitive cells. A _Helix_ whose tentacles had been removed manifested its repulsion to the smell of spirits of turpentine, while another _Helix_, which was unmutilated, did not object to the turpentine being held between its tentacles. Altogether, then, the exact position of the smell-organ in the Helicidae must be considered as not yet thoroughly determined. Simroth holds that the sense of smell is distributed over the whole soft integument, and is especially concentrated in the feelers, and in the neighbourhood of the respiratory orifice.[304] In nearly all marine Mollusca yet examined, the organ of smell or _osphradium_ is in situation intimately connected with the breathing organs, being generally placed near their base, with the object, apparently, of testing the quality of the water before it passes over the branchiae. It consists of a patch of the epithelium, modified in a special manner, and connected by its own nerve with one of the visceral ganglia.