POLYGYRA ALBOLABRIS AND LIMAX MAXIMUS 275 



be unnecessary^ as the foot is well supplied with nerves, and is 

 very sensitive; second, though the tentacles are bent down toward 

 the object on which the animal is moving, I have never seen them 

 touch the object. Furthermore, the tentacular ganglia are anterior 

 to all others, with the single exception of the ganglia of the super- 

 ior tentacles, and are attached by their nerves to the cerebral 

 ganglia, which, taken in connection with the anterior position of 

 the tentacles themselves, corresponds to the position of the olfac- 

 tory organs in vertebrates. When the tentacle is withdrawn, the 

 olfactory sense still exists; the olfactory organ then closely cor- 

 responds to the olfactory organ of fishes. Negatively, the olfac- 

 tory organ certainly does exist; but the nerves at the mouth, 

 which have been considered by some authors as olfactory nerves, 

 are undoubtedly nerves of taste; while the pedal sinus is clearly 

 for the secretion of mucus, which the animal so abundantly 

 exudes while in motion. Taking into consideration the anatomic 

 details of the inferior tentacles, and innumerable observations of 

 the use of these organs by the animal, I have no hesitation in 

 affirming that they are olfactory organs. 



In some forms of Gasteropoda no tentacles exist, and it will be 

 interesting to determine whether in the absence of tentacles the 

 olfactory sense is deficient. In relation to this Albany Hancock,^ 

 says: 



Being engaged at present in the investigation of the anat- 

 omy of some members of this family, my attention was naturally 

 directed to this point, and I think that I have obtained satisfac- 

 tory proof that these hornless animals have really the sense of 

 smell highly developed. The head lobe in the Bullidae is, in fact, 

 nothing else than the dorsal (superior) and labial (inferior) ten- 

 tacles fused in one continuous mass. This Cuvier asserted long 

 ago; and it can be very easily proved on anatomical grounds 

 . . . It may therefore suffice to say at this moment, that 

 the nerves which supply the oral (inferior) and dorsal (superior) 

 tentacles in the Gasteropoda go to this lobe, the former to the 

 anterior and the latter to the posterior portion of it; a pretty clear 

 proof of its real nature. 



Hearing. The so-called auditory organs consist of two trans- 



1 Ann. and mag. nat. hist. 1852. 



