366 PHYSIOLOGY OF THE INVERTEBRATA. 



In the Molliisca there appears to be special organs of taste, 

 in the form of a specific sensory epithelium at the entrance 

 of the buccal cavity. 



In the Cephalcypoda, "the fleshy point of the tongue is 

 undoubtedly a gustatory organ. It is concealed in the 

 anterior angle of the lower jaw, and its rounded surface is 

 covered with numerous soft villosities, which very probably 

 serve as gustatory papillae." 



The olfactory organ of the SrancMogasteropoda has been 

 examined by Dr. J. W. Spengel.* He finds that in Trochus, 

 Tmio, and Vermeius, the so-called " rudimentary gill," or 

 colour gland of T. Williams, is an olfactory organ. This 

 organ consists of a large mass of nervous matter, invested by 

 a layer of epithelium, into which nerve-fibres distinctly pass. 

 Spengel has also proved that the ciliated organs of Gegenbaur 

 in the Pteropoda have an olfactory function. 



Dr. D. Sochaczewerf has also examined the olfactory 

 organs in the Fulmogctsteropoda. In these animals, the 

 tentacula, the organ of Semper, and the pedal gland have 

 each been considered to have the function of an olfactory 

 organ. Sochaczewer has tried the following experiments: 

 («.) Having cut off the tentacula of Helix pomatia, the wound 

 was allowed to heal. The snails were then placed on a flat 

 plate, the edge of which was smeared with turpentine. Both 

 tlie mutilated and unmutilated specimens turned away from 

 the edges. This shows that the tentacula are not the seat of 

 the olfactory organ. (&) The organ of Semper is small in 

 Sdix, Arion, and Limnceus ; but is well developed in Limax. 

 Here it has the form of four or five glandular lobate processes, 

 which are set at the sides of the moath. This organ is 

 ■supplied with four nerve-fibres. The two median are mus- 

 cular in character, while the lateral branches are the proper 

 labiales, which give off, one on either side, a fine nerve-branch 

 to the glandular branches of Semper's organ. The cells of 



* Zeitschrift fur Wiss. Zoologie, vol. 35, p. 333. 

 t Ihid. p. 30. 



