LESSON 77.] NERVOUS SYSTEM IN THE MOLLUSCA. 



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1160. The muscular fibres of the cloak, or mantle, are arranged 

 in flattened bands (Fig. 374, e, e). The mouth and stomach, the liver 

 and the heart, are aggregated in a small mass near the posterior aper- 

 ture of the tunic (d) ; the intestine (c) extends towards the opposite 

 .iperture (a), and terminates in the common cavity of the mantle. 

 The brain and nervous system are seen at f. 



1161. In Salpa polycratica (Fig. 374), the nervous system will 

 be found beautifully developed, of which an enlarged view is given in 



FIG. 374. 



FIG. 375. 



Magnified view of nervous system, 

 8. polycratica. 



Salpa polycratica. 



Fig. 375. The word Salpa is Greek, and means a small fish ; poly- 

 cratica poly, much ; cratica, from kraios, strength. 



By reference to the figure it will be seen that the nervous system 

 consists of two lobes, or ganglia, not separated by an interval of 

 space, but lying one upon the other. All the nerves are, without any 

 exception, distributed from the larger lobe, which is the equivalent of 

 the base of the brain, or infra-oesophageal ganglion (&), and are dis- 

 tributed to all parts of the body ; the analogue of the supra-ossopha- 

 geal ganglion (a) sends off two branches at right angles, which ter- 

 minate in expanded lobes (c, c). Nerves are not given off from this 

 latter lobe, simply because the creature is destitute of organs of 



