12 



NERVES OF THE APLYSIA. 



brain of these animals : it furnishes nerves to the organs of 

 the senses as well as to the neighbouring parts (o), and is 

 continued posteriorly by two inter-ganglionic cords, which em- 

 brace the CEsophagus, and which, at a short distance, unite 

 with a second nervous mass (^), situate beneath the digest- 

 ive tube, and comparable to the posterior pair of ganglia, 



which we remarked when 

 speaking of the acephalous 

 mollusks ; and two small 

 nerves, which arise from the 

 ' brain, unite to form a third 

 ganglion {fg- 4, t), below 

 the origin of the oesophagus. 

 c In other gasteropods, the 

 o aplysicR or sea-hares, for ex- 

 ample, to these ganglia is 

 g joined another {fg. 4, i?), si- 

 tuated among the viscera, 

 and united by two commu- 

 nicating threads to the med- 

 ullary collar which surrounds 

 the oesophagus,, and giving 

 rise to the nerves of the in- 

 testines, liver, branchise, ova- 

 ries, &c. We also find in 

 these mollusks a fifth gan- 

 glion, which is very small, 

 belonging to these latter or- 

 gans. And, in the poulpes 

 and the cuttle-fish (fig. 5). 

 V in which this system acquires 

 its highest degree of de- 

 velopment, the ganglionic 

 parts grouped around the 

 oesophagus, are larger and 

 more complicated ; for the 

 cephalic and post-oesopha- 

 geal ganglia, united in a 

 large cesophageal collar, 

 present laterally a third 



Fig. 4. NERVES OF THE APLYSIA. 



Explanation of Fig. 4. — Nervous system of the aplysia (or sea-hare, as 

 it was called by the ancients), another gasteropod moUusk ; — c. the brain; — 

 0. the nervous collar which surrounds the oesophagus ; — g. the thoracic of 

 posi-OEsophageal ganglia ; — v. the visceral ganglion ; — t. the buccal ganglion. 



