317 



NOTE ON THE NERVOUS SYSTEM OF AMPULLARIA, sp. 

 By R. H. BuRNE, B.A., F.Z.S., etc. 



Read 12 1 A May, 1899. 



Since I have lately had the opportunity of dissecting the nervous 

 system of Ampullaria, sp./ I propose, on account of the ambiguous 

 nature of the relationships of this genus, to point out in the following 

 note the features in which this dissection differs from that described 

 by Bouvier^ in his well-known memoir on the nervous system of 

 Prosobranchs. 



On p. 90 of the paper quoted, Bouvier describes the pedal ganglia 

 and the nerves issuing from them ; he recognizes iive main nerves on 

 each side. Three of these, situated on the median side and distributed 

 to the sole of the foot, have a peculiar importance. The other two are 

 less marked. They lie external to the three larger nerves, and are 

 distributed to the lateral parts of the foot. This, it will be noticed, is 

 an arrangement that bears no resemblance whatever to the scalariform 

 pedal cords of Vivipara — the genus to which, in many respects, 

 Ampullaria appears to be most nearly allied. 



In Ampullaria, sp. {vide figure), each pedal ganglion sends down- 

 wards into the foot a bundle of nerves. One of these far exceeds the 

 others in size. After a short downward course it runs backwards in 

 the substance of the foot, approximating slightly to the median line. 

 In its posterior half it is united to its fellow of the opposite side by 

 a series of four or five very delicate commissures. Lateral and median 

 nerves are given off from the main trunk, especially near its emergence 

 from the pedal ganglion. The lateral nerves, as they approach the 

 margin of the foot, anastomose with one another and also with the 

 extremities of the other nerves that issue directly from the pedal 

 ganglion. In this way the marginal portions of the foot are traversed 

 by an intricate nervous network, with minute ganglionic masses 

 situated at each point where two or more nerves unite. It will be at 

 once noticed that in outward form, this pedal nervous system is almost 

 precisely similar to the scalariform cords of Vivipara. There is, how- 

 ever, this very essential difference between the two : In Vivipara the 

 cords that run longitudinally backwards in the foot and are united at 

 intervals by transverse commissures are ganglionic in nature, and form 

 part of the pedal ganglia ; in Ampullaria they are without ganglion 

 cells, and thus are simply pedal nerves, issuing as in any of the higher 

 gastropods from anteriorly concentrated pedal ganglia. 



^ Belonging to the Eoyal College of Surgeons of England. 



2 Bouvier, " Systeme nerveus . . . des Gasteropodes Prosobranches " : Ann. Sci. 

 Nat. Zoologie, ser. vii, torn, iii (I887j. 



