32 Mr. A. Hancock on the Anatomy of Antiopa Spiuolae. 



Nervous System, — The cephalic or cerebral ganglions are 

 arranged round the oesophagus in the same manner as in Eolis ; 

 there are five pairs, three supra-oesophageal, two infra-oesopha- 

 geal ; the former are very much the larger and nearly of equal 

 dimensions. Of these the two central pairs, the cerebroid (PI. III. 

 fig. 5 a, a) and branchial [b, b), the latter the "cervicaux" of Blan- 

 chard, are almost completely fused, forming two elongated, 

 bilobed masses, one on each side of the median line, — the 

 branchial lying behind the cerebroid, which latter is united by 

 a veiy short commissure to its fellow on the opposite side of the 

 oesophagus. This is exactly similar to what is observed in Eolis ; 

 but in this latter genus the masses being less distinctly bilobed, 

 the constituent parts are not so readily made out. External to 

 these masses, and in close contact with them, are two rounded 

 ganglions, the third or pedial pair {c, c). These lie in a plane 

 a little below the central masses, and are united to them on the 

 under surface. 



The first and largest pair of nerves are given ofi" from the upper 

 surface of the cerebroid ganglions in front, next the median line ; 

 these are the olfactory nerves. Each immediately divides into 

 two portions, — the inner, generally the larger, of which converge, 

 and go to the crest between the dorsal tentacles, where they 

 divide into numerous twigs ; the outer portions diverge a little 

 and enter the bases of the dorsal tentacles, and are there enlarged 

 to form the olfactory ganglions {d, d), which are quite distinct 

 and round, and very little inferior in size to the buccal. The 

 second, third and fourth pairs come from the under side of the 

 front margin of the same ganglions, and supply the lip and 

 channel of the mouth, and probably the oral tentacles. The 

 fourth pair give off at their roots a nervous trunk ; these trunks 

 curve round, one on either side of the oesophagus, and are united 

 to the buccal ganglions ; thus forming the commissure [g) 

 between the supra- and infra- oesophageal nervous centres. The 

 fifth pair issue from the upper surface of the cerebroid ganglions 

 near to their junction with the branchial; these are the optic 

 nerves ; they are very delicate, and are long enough to allow the 

 eye, which is as well developed as in any of the Nudibranchs, to 

 pass a little in front of the ganglions. M. Blanchard represents 

 the eye as almost sessile on the cerebroid ganglion. The sixth, 

 the auditory, I did not detect ; they will undoubtedly be found 

 behind the optic, as described by M. Blanchard. The seventh 

 pair of nerves emerge apparently from the pedial ganglions at 

 their union with the central masses, and supply the skin on the 

 sides of the body in front. The eighth and ninth pairs pass from 

 the outer margin of the pedial ganglions, and go to supply the 

 foot. From the posterior margin of these ganglions emerges a 

 stout nervous trunk (A), which curving under the gullet, com- 



