PHYSIOLOGY OF THE INVERTEBRATA. 367 



the constituent lobes resemble the glandular cells of the 

 salivary glands; in other words, this organ has not an olfactory 

 function, (c) The pedal or foot gland is looked upon by 

 Sochaczewer as an olfactory organ. It is well supplied with 

 nerves ; but experiments are difficult to try in such an 

 organ. 



The olfactory organs of the Ceplmlopoda, are situated near 

 the eyes. They are either depressions or papillas of the 

 integument. The nerves which 

 supply these organs arise from 

 the optic ganglion of the oeso- 

 phageal nerve-ring. 



The auditory organs (Fig. 71) 

 of the Lamellibranchiata con- 

 sist of a pair of vesicles or sacs. ^'O' 7i- 

 These vesicles are filled with a the auditory okgan of Cyclas 

 fluid (enddlymph) containing 2 = capsule or sac b = ciliated 

 otoliths ; and they are attached "P'*""^' "=""=• ' = °'°'^''^- 

 by short nerves to the pedal 



ganglia. In the Mollusca generally, a delicate sensory epi- 

 thelium marks the percipient portion of the inner wall of the 

 auditory sac. 



The auditory organs of the Gasteropoda, as represented by 

 Helix, are in pairs, close to and connected with the pedal 

 "ganglia. Each auditory, organ or otocyst consists of an in- 

 ternally ciliated vesicle or sac containing a fluid and otoliths ; 

 an auditory canal which may communicate with the exterior ; 

 and an auditory nerve from the cerebral ganglia. 



A pair of auditory vesicles are always present in the 

 Pteropoda. 



In the DibraTichiata, the auditory organs are situated in 

 the cavities of the cephalic cartilage. The internal walls of 

 the auditory vesicles in the Octopoda are smooth ; but in the 

 Loligina they are raised into papillse. 



In the Tetrahranchiata, represented by Nautilus, the 

 auditory organs are attached to the pedal ganglia, and are 



