12 



NERVES OF THE APLYSIA. 



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

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

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

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

 with a second nervous mass (g 1 ), situate beneath the digest- 

 >ve 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 (Jig. 4, tf), below 

 the origin of the oasophagus. 

 In other gasteropods, the 

 o aplysice or sea-hares, for ex- 

 ample, to these ganglia is 

 g joined another (jig. 4, t)), 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, branchiae, 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 (Jig. 5), 

 A I jS^^T^\\ v in which this system acquires 



Fig. 4. NERVES OF THE APLYSIA. 



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 oesophageal collar, 

 present laterally a third 



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

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

 p. the nervous collar which surrounds the oesophagus ; g. the thoracic or 

 post-oesophageal ganglia ; v. the visceral ganglion ; t. the buccal ganglion. 



