ORGANS OP SENSE, 19 



pulmonates, or even, as in the oriental Melania and Melanopsis, 

 a large laminated otolite together with small crystalline ones. 

 The anditorjr nerve divides upon the vesicle into a number of 

 branches; and the vesicles are probabl}^ connected with the 

 external world by means of an auditory canal; at least such a 

 canal exists ( according to Ad. Schmidt) in Helix, and Kolliker 

 discovered it in the cephalopods. 



The Pteropoda and Scaphoda are provided with similar hearing- 

 organs. 



Felecypoda (vi, 78). There is a single auditory organ wanting 

 however, in the adult stage in those genei'a which then become 

 fixed; it is found in the neighborhood of the pedal ganglia, or 

 even as in Spha?rium, joined to them. 



J^otwithstanding the existence of hearing organs in the lamel- 

 libranchs is so definitely ascertained, they appear to be entirely 

 insensible to sound, although the Anodonta is tactilely aware of 

 vibrations of the air. 



Olfactory Organs. That the sense of smell is well developed 

 in man}^ mollusks has been experimentally ascertained, but the 

 location of the organ has not Ibeen satisfactorily demonstrated. 

 Moqnin-Tandon relates that a naturalist, observing an Arion 

 (garden-snail) moving in right line towards a pea-pod, from 

 which it was two yards distant, picked up the pod and placed it 

 in his pocket. The animal presently halted, and raised its head 

 and directed its horns towards the now unattainable luxury. 

 The pod was now replaced on the earth in another direction and 

 hid by a stone, but the animal was not at fault and turned again 

 in quest of its food. A new change of position of the morsel 

 determined another itinerary, and finally the Arion was allowed 

 to enjoy its well-earned meal. Fischer has witnessed the rapidity 

 with which numbers of Nassa reticulata assemble around the 

 putrefied carcass of a fish when thrown into the water. They 

 make towards it immediately^, from all quarters. On the English 

 coast Fusus antiquus is gathered by means of carrion. Whelks 

 (Buccinum undatuiii) are very troublesome to the lobster-fishers, 

 for they often devour the bait, and at St. Margaret 's-at-Cliffe, on 

 the Kentish coast (England), the lobster pots are sometimes 

 drawn up, one after the other baitless, and full of these greedy 

 mollusks (Lovell^. Even some lamellibranchs appear, by their 

 partialit}^ for putrefying fiesh to possess a sense of odor. 



The lamellated tentacles or rhinophores of some of the opis- 

 thobranchiate gastropods have been supposed b}^ Hancock and 

 Embleton to be olfactory organs (vi, 79). Their nerve is large 

 and provided with a large ganglionic swelling. They are 

 retractile within a special cavity. In the pulmonta geophila, 

 Moquin-Tandon supposes the bulb-like extremity of the ocular 

 tentacles to possess olfactor}^ functions : he finds that after 



