DIGITAL AND OPHTHALMIC TENTACLES. 775 



nerve, von Jhering also confirmed Valenciennes in these words : — " Nach innen und unten 

 vom Sehnerven entspringen vom oberen Theil des vorderen Suboesophagealstranges der 



Geruchsnerv und der Nerv des vorderen, unteren oder ventralen Augentakel." This 



of course is a very broad statement, and in fact the true olfactory nerve does lie below 

 the optic ganglion, but it does not arise from the anterior (pedal) commissure (cf my 

 PI. LXXXI. fig. C). 



Pelseneer' regarded the ophthalmic tentacles of Nautilus as belonging essentially to 

 the head, and as homologues of the labial and nuchal cephalic tentacles of Gastropoda, 

 and therefore not honiodynamous with the digital tentacles of Nautilus. While advocating 

 the theory of the pedal nature of Cephalopod arms in general, he insists on the cephalic 

 nature of the ophthalmic tentacles of Nautilus, saying in a foot-note : " II est inexact de 

 dire, comme von Jhering, que le tentacule ophthalmique anterieur est innerve par le 

 ganglion infra-oesophagien anterieur. Tout comme le nerf olfactif, le nerf du tentacule 

 ophthalmique anterieur sort de la partie laterale extreme du ganglion supra-cesophagien, 

 ainsi que le montrent les figures precit^es de Valenciennes." 



It is therefore quite clear that the ophthalmic tentacles of Nautilus occupy a crucial 

 position as between head and foot, and it is the more desirable to ascertain the exact 

 origin of their nerves. The most recent author who has dealt with this matter is 

 Dr L. E. Griffin'^, who describes an accessoiy nerve-trunk associated with the axial nerve- 

 trunk traversing the body of the tentacle, and adds that " the nerves of the two ocular 

 tentacles of each side are branches of a nerve which comes off from the pedal ganglion 

 near the outer end, which also sends branches to the hood." 



According to my own observations Dr Griffin's statement comes nearer to the truth 

 than any other relating to this point with which I am acquainted, but I do not agree 

 with him that the ophthalmic nerves are branches of the hood-nerve. 



The ophthalmic nerves in fact arise by independent roots from the dorsal boi-der 

 of the pedal ganglion'. The anterior ophthalmic nerve arises close behind the capitular 

 (hood) nerve, but is surrounded by its o\vn perineurium, and proceeds upwards and 

 slightly forwards to the base of the tentacles (PI. LXXXII. fig. 6). The posterior 

 ophthalmic nerve again arises independently, close behind its colleague and holds 

 a pronounced recurrent course, passing backwards to its tentacle in the wall of a sinus 

 in which the optic ganglion lies. The posterior ophthalmic nerve does therefore not arise 

 dorsad of the optic nerve, but it passes backwards from its origin in the pedal ganglion 

 (PI. LXXXII. fig. 6). The position of the ophthalmic nerves in relation to the digital 

 nerves shows that the ophthalmic tentacles are in sequence with the digital tentacles, 

 and that the posterior ophthalmic tentacle is the first, the anterior ophthalmic tentacle 

 the second, and the capitular (first digital) tentacle the third member of a continuous 

 morphological series, the remaining digital tentacles following in their due order. 



In the diagrams of transverse sections on PI. LXXXI. the ophthalmic tentacles are 



' Pelseneer, P., " Sur la valeur morphologique des bras et la compositiou du systfeine nerveux central des 

 C^phalopodes." Arch. Biol. Vol. viii. 1888, see p. 730. 



- (irillin, L. E., "Notes on the tentacles of Nautilus p(impiiiu,v." Johns Hopkins Univ. Circ. Vol. xviii. 

 Nov. 1898. 



' For the present I use the term "pedal" in this connection as being less unwieldy and less inaccurate 

 than " infra-oesophageal." It might be called by an indifferent name, such as " coronal ganglion." " Brachial 

 ganglion" implies too much. "Tentacular ganglion" would also mislead. 



