774 DIGITAL AND OPHTHALMIC TENTACLES. 



In my paper on this subject (1897) I added the following remarks: — ■" The presence 

 of accessory olfactory tentacles in Nautilus can, I think, be related to an essential 

 bionomical difference between the existing Tetrabranchiata and the Dibranchiata. Nautilus 



finds its food chiefly by the sense of smell, while the Dibranchiata with their 



remarkably perfect eyes pursue their quarry by the sense of sight. This difference 



is further emphasised by the different modes adopted by the natives for trapping these 

 animals. 



" One of the surest ways of obtaining Nautilus, and in fact the method by which 

 I have obtained most of my specimens at Lifu, is to bait the fish-basket with the 



cooked and bruised exoskeleton of Palinurus wrapped up in cocoa-nut fibre like 



a small parcel and placed in the fish-trap overnight. There is nothing to be seen but 



something to be smelt, and by this means I have obtained as many as ten 



Nautilus at one time. For taking Octopus the natives of Lifu employ a very different 

 method. A rounded oval piece of stone backed by a well-fitting piece of the shell of 

 a species of Cypraea, to which are added pieces of leaf to simulate legs and tail, is 

 dangled along the surface of the water at the end of a line. The natives say that 



the Octopus mistakes this for a rat, against which it has a special grudge; but 



the fact remains that Octopus attacks this singular non-scented contrivance and so is 

 captured." The Lifuan name for this simple apparatus is "athy." 



One of the most interesting points about the ophthalmic tentacles concerns their 

 innervation, regarding which there has been serious disagreement among zoologists, but 

 I hope to show in this matter that the facts of the case are beyond the reach of 

 controversy. Owen's figure (1832) of the central and peripheral nervous system of 

 Nautilus conveys an excellent general idea of its main characters, but is too diagram- 

 matic in its representation of details to be of much assistance at this particular juncture. 

 Valenciennes (1841, p. 288, PL vin. fig. 2) described the nerves of the ophthalmic 

 tentacles as arising from the cephalic ganglionic ring, separated from each other on each 

 side by a wide interval which is occupied by the optic and true olfactory nerves, so 

 that according to him the nerve which supplies the posterior ophthalmic tentacle arises 

 dorsad and mediad of the optic nerve. Valenciennes appears to have overlooked the 

 buccal or stomatogastric nerves, of which there are two pairs arising from the cerebral 

 (supra-oesophageal) commissure, and hence probably misinterpreted one of the latter as 

 the nerve to the posterior ophthalmic tentacle (cf. PI. LXXXIII. figg. 28 and 29). 

 Nevertheless von Jhering 1 , who was the first to note the existence of a stomatogastric 

 or " sympathetic " nervous system in Nautilus, confirmed Valenciennes' account of the nerves 

 to the ophthalmic tentacles, which we may be allowed to call the ophthalmic nerves in 

 place of a better name although it is of course open to misinterpretation ; but I am 

 not prepared to suggest a new name. Von Jhering says that the posterior ophthalmic 

 nerve is the last nerve which leaves the supra-oesophageal ganglion dorsad of the optic 

 nerve. As a matter of fact this last cerebral nerve is the second buccal or stomato- 

 gastric nerve which von Jhering overlooked. With regard to the anterior ophthalmic 



1 Jhering, H. v., " Vergleichende Anatomie des Nervensystemes und Phylogenie der Mollusken," Leipzig, 

 1877, pp. 262 and 2134. Von Jhering's account of the stomatogastric system has been essentially corrected and 

 amplified by Mr J. Graham Kerr (op. cit. 1895), whose description of these nerves I can confirm. 



