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running to the oesophagus. A single nerve from its posterior, ventral, 

 median edge runs to the posterior part of the oesophagus. 



Each branchial nerve divides into two soon after it leaves the cere- 

 bral ganglion. The outer division sends two branches into the outer 

 part of each branchia, and to the operculum and pseudoperculum 

 stems; the inner bears a large ganglion soon after it leaves the outer 

 division, and sends one nerve to the inner side of each branchia. 1 

 could find no nerves given off from this division to the operculum and 

 pseudoperculum. 



The cerebral ganglion gives off, on either side, a large commissure, 

 which passes down around the oesophagus, and into the large ventral 

 ganglion of the corresponding side. 



The ventral nervous system is made up of two long nerves , one 

 on either side of the body, running to its extreme posterior end. In 

 each segment the chain is swollen into a ganglion , the anterior pair 

 of ganglia — those which receive the oesophageal commissures — , 

 being much the largest of any. 



From then backward, the ganglia gradually decrease in size. The 

 anterior pair are connected with each other by three cross commissu- 

 res, while each segment behind this, as far back, at least, as the 

 middle of the body, has one commissure. Farther back than this I 

 was unable to trace them . the small size of the nerves together with 

 their resistance to coloring reagents, rendering their detection very 

 difficult. Nerves are given off to the hypoderm, the mantle etc. from 

 these ganglia. 



The nerves are composed entirely of nerve fibres: the ganglia, 

 of nerve fibres , with more or fewer nerve cells. About two thirds of 

 the mass of the cerebral ganglion is made up of cells, while the inner 

 portion is composed of fibres. The other ganglia contain but a few 

 cells , arranged on their outer surface. 



The tubular fibres are not so highly developed in S. (Hat/thus . as 

 in allied annelids. Instead of running through the first pair of ventral 

 ganglia, and through the cross commissures connecting them, the) 

 reach only to the posterior end of these ganglia, when they thin out 

 and disappear. Tow r ard the posterior end of the body, however, they 

 have a diameter nearly twice as great as the nerve cord proper. 



At its posterior end, the dorsal portion of the cerebral ganglion is 

 prolonged into a most remarkable process; from the dorsal, posterior 

 corner on either side, a large lobe passes outward and backward, for 

 a short distance, and then, bending suddenly downward, passes into 

 the first ventral ganglion. The diagrams, Figs. 1 and 2, show the re- 

 lations of the various parts. Fig. 1 is a diagram of the ganglion and 



