CH. VII] SNAILS AND SLUGS 225 



to this view. The pedal gland 1 has by many been claimed 

 as an olfactory organ: undoubtedly the character of its 

 epithelial lining points to sensory functions of some sort, 

 in addition to that of secreting mucus to which reference 

 has already been made ; it has not however been proved 

 that the special sense here located is that of smell. Closely 

 allied to smell is the sense of taste : this Simroth 2 considers 

 to be diffused over the surface of the body with special 

 developments under the lips and buccal membrane, in 

 which situations special groups of sensory cells have been 

 discovered by Smidt 3 . 



The otocysts have been assumed to be the auditory 

 organs, but no evidence has been adduced to show that 

 these animals are sensitive to those vibrations which 

 produce in us the sensation of a sound. It is far more 

 probable that these structures enable their possessor to 

 determine the position of the body during locomotion, and 

 to maintain its balance. Situated as the two otocysts are 

 upon the ventral side of the pedal components of the 

 suboesophageal ganglion mass, direct experiment upon them 

 is impossible. Each cyst is a thin transparent sac about 

 015 mm. in diameter; it is lined internally with sensory 

 and ciliated epithelial cells, and contains a fluid in which are 

 suspended numerous minute calcareous bodies (otoconia) ; 

 these are oval in shape and contain a " nucleus." During 

 life the otoconia are maintained in constant motion by the 



1 Sochaczewer, Zeit. wiss. Zool. xxxv. and xxxvi. 1882; cf. Andre, 

 Rev. Suisse Zool. 1894. 



2 Zool. Anz. 1882. 



3 Smidt, Anat. Anz. xvi. ; cf. Gain, Journ. of Conch, vi. 



L, 15 



