518 H. p. KJERSCHOW AGERSBORG 



A'ibratile cilia, and so placed on the head as easily to receive 

 impression from any odorous particles that may be mingled 

 with the circumambient water.' Likewise, Jeffreys (1869) 

 claims olfaction for the dorsal tentacles, but he says : ' . . . olfac- 

 tion m these animals probably is not so much to assist in the 

 discovery of alimentary matters, as to give warning of the 

 unhealthy state of the surrounding medium, arising from 

 putrescence or other causes. . . . and its outer surface, in all 

 the nudibranchs, is provided with vibratile cilia.' The tentacles 

 in M. leonina, however, are not ciliated. Bergh adopts 

 the term ' rhinophoria ' for the dorsal tentacles, not only 

 indicating in that way the function, but he claims, in fact 

 olfaction to be their function. Later writers, Lang 

 (1896 : 48, 103), Sedgwick (1898 : 366), seem to agree on this 

 point. Copeland (1918 : 177-227) demonstrated experimentally 

 that the monotocardiate prosobranchs Alectrion obsoleta 

 and Busy con canaliculatum respond to stimulations 

 by dilute food extracts and materials emanating from distant 

 food ; he thinks that the snails do not find food by coming 

 upon it accidentally, but are directed to it by movements 

 brought about through stimulations of the olfactory organs 

 with odorous substances conducted to the receptor in varying 

 concentrations by the moving siphon. By means of an olfactory 

 apparatus consisting of a single organ of smell associated with 

 a siphon terminating in a shifting ' nostril ', for sampling the 

 surrounding water and its contents, the snail is as successfully 

 directed toward distant food as an animal which, like the 

 dogfish, possesses paired olfactory organs and fixed nostrils. 

 After the osphradium in Busycon was destroyed the snail 

 failed to respond to dilute food materials, but a year later, 

 when the lamellae of the organ were partly regenerated, the 

 scenting responses returned. The osphradium, therefore, is an 

 olfactory organ. This author claims further that taste in the 

 snail (Busycon) is a diffused sense as compared with olfac- 

 tion, and that a large portion of the surface of the snail possesses 

 this sense. But Arey (1918 : 531) distrusts the capability of 

 snails to analyse chemical stimuli as discrete sensations, and 

 thinks that it would be safer to avoid referring in their case 



