184 IMessrs. Hancock and Einbleton on the Anatomy o/Eolis. 



addition to these_, there is a pair of ganglia, e e, at the base of the 

 dorsal tentacles, which we call olfactory ; and we have seen what 

 we take to be other ganglia, but of these we shall speak further on. 



The nervous centres intercommunicate by the following com- 

 missures. A short broad one, f, unites the first pair of supra- 

 oesophageal, and a similar though smaller, g, the first pair of 

 infra- oesophageal ; these have been already noticed ; then the 

 lateral supra-oesophageal are united to the first or anterior or 

 cerebral by a broad flat band, h, so short that the ganglia appear 

 to be continuous with each other. Next we have three nervous 

 bands or collars, concentrically arranged, inclosing the oesopha- 

 gus, and serving to complete the connexions of the supra-oeso- 

 phageal ganglia with each other, and to bring them into asso- 

 ciation with the infra- oesophageal. First, the innermost or 

 thickest collar, z, lies close to the oesophageal wall, and is com- 

 posed of four or five distinct nervous filaments running parallel 

 to each other, and connecting together the posterior borders of 

 the two lateral supra-oesophageal masses. Second, a slender, 

 delicate collar, j, lies next outside, much wider than the former, 

 and uniting the posterior and outer parts of the first pair of 

 supra-oesophageal ganglia, it comes out from the under surface 

 of these bodies and runs under the second or lateral ganglia. 

 The existence of this collar or commissure between the posterior 

 parts of the median cerebral ganglia, whilst their anterior parts 

 are united by the anterior median commissure, seems to confirm 

 the impression we received at first sight, that the cerebral ganglia 

 are each of them double centres. It will be observed that the 

 two last-described oesophageal collars are not attached in any 

 way to the infra- oesophageal ganglia. The third or outermost 

 collar, k, however establishes a communication between the first 

 or median supra-oesophageal and the first infra-oesophageal gan- 

 glia. This is a strong band, being little inferior in size to the 

 first, of uniform texture, and lying just outside of the second col- 

 lar, and in contact with it, it is the widest of the three. In front 

 it is attached to the under part of the outer border of the first 

 cerebral ganglia, considerably in advance of the coming off of the 

 second collar ; from this part it is traced backwards under the 

 lateral supra-ossophageal into the external end of the buccal 

 ganglia. 



The nerves vary a good deal in size, and we have been able to 

 trace thirty-three pairs ; of these, twenty-one come off" from the 

 supra-oesophageal ganglia, six from the infra-oesophageal, and 

 five from the commissures. There is also a large pair which 

 comes out from the buccal mass from an obscure ganglion im- 

 bedded in the muscular tissue, and a small nerve, apparently 

 single, that separates from the middle collar of the oesophagus, 



