5 2 Shell Life 



of a particular pitch by rubbing his finger along the 

 glass. 



The seat of hearing resides in a pair of closed cells 

 called otocysts filled with a clear fluid in which are 

 suspended one or more grains of chalky material 

 called otoliths, and lined with cilia. These otoliths 

 may be very numerous, and they are agitated by 

 sounds in the immediate neighbourhood of the 

 animal. These vibrations act upon the cilia which 

 convey impressions by the acoustic nerve to the 

 cerebral or the pedal ganglia. 



The most important of the senses to the Mollusca 

 is apparently that of smell. It is quite certain that 

 it is much farther-reaching than either vision or 

 hearing, and more constantly in use. Great numbers 

 of carnivorous mollusks, such as whelks, dog-whelks, 

 and naticas, are found in lobster-pots baited with 

 "high" fish which they have smelled through the 

 waters. Slugs appear to be highly endowed with 

 this sense. Apples and bean-pods dropped in the 

 centre of a road will draw slugs from the hedges on 

 either side. As soon as certain species of Agaric 

 come up in the woods slugs bear down upon them 

 and commence feeding upon them. They are also 

 able to locate a dish of milk in a dairy and proceed 

 to drink from it. Of course, this sense is more highly 

 developed in the active univalves than in the more 

 or less sedentary bivalves, but the agile Pea-shells 

 (Pisidmin) are not deficient in it, as shown by the 

 numbers that swarm over any dead animal that has 

 been thrown into a ditch or pond inhabited by them. 

 Some of the Sea-slugs have a sj^ecial pair of antennae 

 furnished with projecting plates which are believed 



