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



the remaining ganglia together with their commissures and col- 

 lars, are the repi-esentatives of the medulla oblongata and spinal 

 cord of the higher animals. 



We do not discern in Eolis anything at all analogous to the 

 sympathetic system of the higher animals. 



In the nervous system again we are sorry to be compelled to 

 be at issue with M. de Quatrefages, who states in his paper that 

 " toutes les grandes masses nerveuses sont reunies au-dessus de 

 I'oesophage et d'elles seules emaneut directement les nerfs qui se 

 rendent dans toutes les parties du corps." Subsequently how- 

 ever he points out the presence of a single small ganglion below 

 the CEsophagus, from which small nervous twigs are given off to 

 the mouth and digestive tube. The incorrectness of these and 

 other observations we hope to have rectified. Further, M. de 

 Quatrefages makes out only one nervous oesophageal ring ; we 

 have over and over again seen and verified the three repi*esented 

 in our plate. The nerves of vegetative life he derives from the 

 same ganglia that give off the nerves of relation, and points this 

 out as an interesting fact. The rule with two or three excep- 

 tions appears to be, that the two sets of nerves have two appro- 

 priately distinct sets of ganglionic centres, viz. the infra- oesopha- 

 geal for vegetative life, and the supra-oesophageal for the life of 

 relation,. which is agreeable to analogy. With regard to the num- 

 ber and arrangement of the nerves, we find M. de Quatrefages to 

 be again in confusion. His number is very far short of the full 

 complement, and he has traced scarcely any to their proper de- 

 stination. We observe that he gives to the optic nerves a gan- 

 glionic swelling which we have never seen, and omits the olfac- 

 tory ganglion, which may be seen even during life in the more 

 transparent species. 



We do not understand M. de Nordmann's account of the ner- 

 vous system. It is possible that in that section of the genus 

 Eolis to which Tergij)es belongs, the nervous system may differ 

 from that of the other divisions, but w^e should be surprised to 

 find it so different from that of those we have dissected, as it is 

 represented in M. de Nordmann's paper. 



The Senses. 



The organs of the senses appear to be as highly developed in 

 Eolis as in any other of the Gasteropods. The sense of touch is 

 spread over the whole surface of the body, including the foot, 

 the tentacles, and the branchial papillse, which last are so ex- 

 tremely sensitive as to respond to the slightest undulations of the 

 water around them. Many of the species indeed are so alive to 

 such impressions, that it becomes a matter of difficulty to observe 

 their habits, and even their natural form, since on the slightest 



