142 JOURNAL OF ENTOMOLOGY AND ZOOLOGY 



species, and all that conld be seen in the sections were occa- 

 sional very minnte ganglia. The gastro-oesophageal ganglia 

 which are described as occurring on the anterior border of the 

 buccal ganglia in typical Dorididae, are apparently completely 

 fused with the buccal, which are regularly ovoid in shape and 

 show no protuberances or other trace of the gastro-cesophageal 

 ganglia, excepting the single nerve. 



The olfactory ganglia, which are about 150 microns in their 

 longest diameter, are closely attached to the upper, anterior 

 border of the cereln-al. They give off a single pair of large 

 nerves, the olfactory. These go forwards for some distance 

 and pass through the muscles of the body wall, but instead of 

 entering the rhinophores directly, go downward and then bend 

 sharply, thus making an S-shaped bend in their course. This 

 is undoubtedly because of the retractility of the rhinophores, 

 all of the observations being of necessity made on retracted 

 rhinophores, as the animal withdraws them upon the slightest 

 disturbance. Within the trunk of the rhinophore in the con- 

 tracted condition, the nerve has a knotted and twisted appear- 

 ance. 



The cereliro-pleural ganglia are by far the largest, measur- 

 ing nearly .5 mm. lengthwise. They are roughly rectangular 

 in shape, and, as has been stated, appear from the upper side 

 as a single pair of ganglia, liut on the lower side are divided 

 transversely into two lobes. In section also they show a trans- 

 verse division into two centers. They are connected dorsally 

 by a large, very short, cerebro-pleural commissure, which con- 

 tains fibres anteriorly from the cerebral and posteriorly from 

 the iileural portions of the ganglia. Ventrally they are joined 

 by the visceral commissure, which bears the visceral ganglia 

 and has its origin on the under side of the posterior part of 

 the pleural ganglia. Besides the nerves of the rhinophores, 

 eyes, and otocysts, the cerebro-pleural ganglia give off eight 

 pairs of nerves. Five of these, which are given off close to- 

 gether on tlie anterior lateral border, may be said to arise 

 from the cerebral ganglion. The nerves numbered 2, 3, 5, 6 in 

 the figure all give branches to the muscles around the mouth, 



