196 MR T. J. EVANS ON 



The Nervous System. (Fig. 7.) 



The brain of Bathydoris broadly resembles that of the Dorids, but with much less 

 concentration of the ganglia. It lies on the top of the buccal bulb, the cerebral, 

 pleural, and pedal pairs being quite separate, but lying close together. As fig. 7 shows, 

 the ganglia are asymmetrical in shape and disposition. Each cerebral ganglion (e.g.) 

 gives off four nerves from its anterior edge which go to the lips and oral tentacles, 

 dividing as they go into a number of smaller nerves. The last bifurcations have small 

 ganglionic swellings at the point of division, as in some Tectibranchs. On the posterior 

 edge of the dorsal surface of the cerebral ganglion stands a small, almost sessile, 

 proximal rhinophorial ganglion (p.rh.g.) which sends a stout nerve (rh.n.) to the dorsal 

 tentacle. A distal rhinophorial ganglion swelling (not shown) marks the point of sub- 

 division of the rhinophorial nerve as it enters the tentacle. No sub-cerebral commissure 

 was found, so that the cerebrals are connected together below the alimentary tube by 

 the stomato-gastric loop (s.g.l.) only. The pedal ganglia (ped.g.) are connected by a 

 stout pedal (ped.com.) and a slender parapedal commissure (p. ped.com.). In the notch 

 between the pleural and pedal ganglia of the right side is placed a small genital ganglion 

 (gen.g.) which is broadly united to the pedal and connected with the pleural by a band 

 of fibres from its lower aspect. From it four nerves go to the genitalia, both male 

 and female, over the surface of which they distribute themselves with a number of local 

 ganglionations on their courses. 



The pleural ganglia (pl.g.) give off two main lateral nerves on each side which 

 supply the whole of the dorsal integument, with the exception of the anterior region 

 which receives a number of very fine nerves from the pleurals not shown in the figure. 

 The longer pair of pleural nerves pass back to the anal region, where they anastomose 

 with each other and with a visceral nerve (br.n.) from the under surface of the right 

 pleural ganglion. From the ganglia on this plexus the gills are supplied as in Doris 

 tuberculata. The visceral ganglion, so obvious on the under side of the right pleural 

 ganglion of Doris, is not represented as a discrete mass in Bathydoris. The visceral 

 ganglion of Doris would appear to include the visceral centres as well as the penial 

 centre usually associated with the pedal. In Bathydoris, however, the genital centres 

 of the visceral seem to be segregated from the rest and to be associated with the penial 

 centre on the pedal to form a special genital ganglion. The long, finely ganglionated 

 visceral loop (v.l., v. I.') about the middle of its course sends backwards the chief visceral 

 nerve (v.n.), which, after giving a branch to the gastro-oesophageal anastomosis on the 

 stomach and liver, continues its course as the reno-cardiac. Two delicate nerves from 

 the pleuro-pedal angle (see diagram) supply the branches of the aorta. The stomato- 

 gastric ganglia (st.g.g.) are relatively very large, but their size is not surprising when 

 we remember the dimensions and muscular complexity of the buccal mechanism which 

 they innervate. The inequality in length of the two cerebro-buccal connectives is pro- 

 bably the result of the sharp sinistral bend of the oesophagus. There are no separate 



