XXViii INTRODUCTION. [CH. 



Organs of sight. The eyes of a Cuttle are more perfect 

 than those of many kinds of fish ; but the so-called eyes 

 of land-snails are supposed to be only organs of touch 

 and not of vision, although endued with a greater sensi- 

 bility than the tentacles which support them. The 

 coloured bulbs which fringe the mantle of a Scallop are 

 also called eyes ; but their structure is very simple. 

 According to Mr. Lea, several kinds of Unio are sensi- 

 tive to light. These organs are entirely wanting in many 

 of the Mollusca, and even in some species of genera which 

 usually have eyes. 



Hearing. In the Pectinibranch Mollusca the contents 

 of the auditory capsules consist of spherical ear-stones, 

 which in every respect but that of form are similar to 

 the otolites of fishes. In the Pulmonobranch Mollusca 

 they are called octoconia and consist of a chalky pulp, 

 which is separable into minute elliptical granules. Frey 

 has observed organs of hearing in many of the land 

 and freshwater Mollusca, both univalve and bivalve. He 

 counted as many as 200 otolites of different sizes in one of 

 the auditory vessels (of which there were two) in an adult 

 snail. In Sphcerium (or Cyclas) each individual appears 

 to have never more than a single otolite. He believes 

 that these bodies are formed by a subcrystallization of 

 the liquid contained in the auditory vessels. 



Smell. In the Helicidce, or land-snails, this sense is 

 supposed to lie in the bulbs which surmount their ten- 

 tacles. It is probable that the carnivorous or zoophagous 

 Mollusks have the power of scenting out their prey or 

 food. Quantities of the common " almond- whelk " of 

 dealers in shell-fish (Fusus antiquus) are procured on 

 the Cheshire coast by the fishermen placing a dead dog 

 on the sands at low-water mark during spring tides. 

 The bait is then completely covered with stones, which 



