Messrs. Hancock and Embleton on the Anatomy o/Eolis. 191 



separated from the main stem and become inclosed in a sheath 

 of their own, and this mode of division appears to be carried on 

 to a very minute degree. We have not been able to detect the 

 manner in which the nerves actually terminate ; certainly we have 

 seen nothing to warrant the description and the figures of M. de 

 Quatrefages relative to this particular. 



On taking a review of the nervous system of Eolis, we are at 

 once struck with the high grade of development, and with the 

 symmetrical arrangement that obtains in it ; the heterogangliate 

 character applicable to many gasteropodous mollusks being, so far 

 as our researches have led us, inapplicable to this more elevated 

 being. The nervous centres are closely concentrated around the 

 oesophagus, and there exists a sufficient correspondence between 

 them and the same organs in the Cephalopoda to enable us con- 

 fidently to compare them ; indeed we have every reason to think 

 that we recognise in them the homologues of the principal masses 

 of the nervous centres of the Vertebrata. 



If we turn to Professor Owen^s memoir on the Pearly Nau- 

 tilus, pi. 7. fig. 1, in which the nervous system is represented, 

 we find that the supra-oesophageal mass or brain together with 

 the attached optic lobes, taken in conjunction with the anterior 

 (Esophageal ring formed by the union of two ganglia, corre- 

 sponds to the anterior supra-oesophageal ganglia of Eulis with 

 the slender or middle collar round the oesophagus, since they 

 give off nerves which go to supply analogous parts, viz. the eyes, 

 tentacles, lips, &c. The posterior oesophageal ring of the Nau- 

 tilus to a great extent represents in the same w^ay the lateral 

 supra-oesophageal ganglia of Eolis, miited with all the infra- 

 oesophageal ganglia and the two large collars or commissures 

 together. 



At fig. 3, same plate. Professor Owen gives a view of the ner- 

 vous system of the Sepia officinalis ; the homology is equally di- 

 stinct as in the former case, only the parts are more concentrated ; 

 still they serve to lead us on more easily to compare the ganglia 

 of Eolis with the several divisions of the more highly-developed 

 nervous centres of the Vertebrata. In Eolis we see that certain 

 nerves of relation — of special and conmion sensation, and their 

 corresponding nerves of motion, voluntary or reflex — are in con- 

 nexion only with the two pairs of supra-oesophageal ganglia. 

 The olfactory and optic nerves, and numerous others to the lips, 

 mouth, tentacles and side of head and back, are thus attached ; 

 hence we infer that the anterior part of the supra-oesophageal 

 ganglia may be in some measure compared, though not perhaps 

 quite accuratel}^, to the cerebrum and optic lobes of the Verte- 

 brata ; at all events these are the only parts to which they corre- 

 spond. The posterior parts of the median cerebral ganglia, and 



