584 Miscellaneous. 



appear to be nothing more than a strong branch from them. This 

 is, with but slight difference, the arrangement observable in the 

 Placophores, in which the cerebro-pedal link is quite separated 

 from the pedio-pallial {Acanthopleura salamander, according to 

 Herr von Jhering, A. Savatieri), and where the visceral commissure is 

 formed, following the hypothesis of Herr Eiitschli, by the median and 

 ventral fusion of the two symmetrically situated stomachal nerves 

 {Ohiton fascicidatus and Ch. maguijtcus, according to M. HaUer ; 

 C. cinereiis, according to Herr von Jhering). 



The " scalariform nervous cords " are remarkable for the gan- 

 glionic projection, in the form of a very elongated horn, which both 

 exhibit in front of their most anterior commissure. This horn 

 presents along its whole length, notably on its outer side, a broad 

 and deep furrow, which is continued upon the cords and which 

 divides each of them into an \ipper pallial portion and a lower 

 pedal ; the cerebro-pallial link arises at the end of the pedal portion. 



The pedal portion, behind the great anterior commissure, presents 

 the usual accessory commissures and gives origin to numerous 

 nerves to the lower surface of the foot ; the pallial portion has no 

 commissures, it siTpplies the mantle, the columellar muscle, the 

 muscles of the upper surface of the foot, and probably also the 

 epipodium. The pallial portion, in other words, behaves exactly 

 like the pallial cords of the Placophores, the pedal portion like the 

 pedal cords of these latter — so much so that the pallio-pedal cords 

 of Pleurotomaria ought to be considered as the result of con- 

 crescence * of the pedal cords and the ganriVionic jwrtion of the 

 pallial cords f which one observes on each side in the Placophores. 



To summarize : Pleurotomaria presents the first stage of a gan- 

 glionic concentration, which is more and more accentuated as one 

 rises in the scale of mollusks. In Haliotis and T'roclms the cords 

 of the foot arc composed, as has been very justly maintained by 

 M. de Lacaze-Duthiers and by 3tl. Boutan, of a superior pallial and 

 an inferior pedal portion ; but the pallial portion tends to isolate 

 itself under the form of a ganglionic swelling situate in front at 

 the origins of the visceral commissure. In the Pissurellida^ the 

 same arrangement exists, but the cords are shorter and, in conse- 

 quence, more condensed. In Patella, Nerites, Ci/clojihora, Paludina, 

 and Cypraa the scalariform pedal cords always persist, but the 

 pallial portion is isolated in the form of distinct ganglia ; in other 

 Gastcropods the pedal cords, like the pallial, are condensed in the 

 form of ovoid ganglionic masses. — Vomptts Rendus, 18"J7, t. cxxiv. 

 pp. 695-G97. 



* According: to Hirren Tliiele and Plate numerous anastomotic nerves 

 attach the pallial to the pedal cords in certain Placoplioi-es ; this is a first 

 step towards the concrescence roalizeJ in Pleurotomaria. 



t As Herren von Jhering and Biitsclili have shown, the ]>allial cords of 

 Placophores are nothing more than the pallial ganglia iused with the 

 great pallial nerve. As in other Gasteropoda, each great pallial nerve 

 anastomoses aljove the inte-'^tine with its fellow of the opposite side. 



