THE NERYOUS SYSTEM OF THE MOLLUSCA. 183 



in these preparations. Thus the elements a and a were differ- 

 entiated in one preparation, h and V in another, and so on. 



Of all the ganglia examined, the best results were obtained 

 with the pleural. In them the finer branchings of the cells were 

 very apparent; and figs. 3, 4, 5, and 6 show the kinds of cells 

 met with — fig. 3 a and fig. 4 being o£ the type already met with 

 in the buccal ganglia, with branching processes and axis-fibre 

 running to a nerve. Pig. 3 h is apparently a " co-ordinating " 

 cell, with simple arboreseence. Various fibres entering the 

 pleural ganglia were seen to break up and end within them in 

 fine branches ; and the same was observed in the cerebral and 

 pedal ganglia, which require further investigation. A series of 

 fibres running across the two pedal ganglia and giving off fine 

 branches, a plexus of nervous elements on the nerve near the 

 ganglia, and various isolated facts of similar nature were noted, 

 but not fully worked out. 



The two visceral and the single abdominal ganglia present in 

 some Gastropods are in Aplysia represented by two {cf. fig. 1) 

 which might represent either the right visceral and abdominal 

 or the two viscerals, the abdominal having disappeared. One 

 of the preparations of this complex, however, showed what 

 appeared to be a group of small deeply-stained cells just within 

 one of the ganglia (fig. 7, a) ; and it appears to me possible that 

 this may represent a degenerated abdominal ganglion. 



The other cells of these ganglia (fig. 7, I) were of the type 

 already met with. Fibres were seen entering and breaking up 

 within the ganglia (fig. 7, c), but their connexions were not 

 traced ; and a number of fibres (fig. 7, cl) were seen to pass over 

 the ganglia. 



Periplieral Nervous System. 



"With this some satisfactory results were in Aplysia obtained by 

 the methylene-blue method. 



Fig. 8 represents a section of a piece of tissue cut out of the 

 side of the body, and shows the presence of long sensory cells (c) 

 with a slight expansion at a varying distance from the epithelium, 

 and a nucleus (ii) which stains deeper than the cell-body. Their 

 mode of termination in the epithelium (fig. 8, c) was observed 

 in thin sections. A number of deeply stained fibres were 

 observed just beneath the epithelium (pi), with occasionally 

 a related nucleated cell {n). These structures may represent 

 a hypodermal nerve-plexus similar to that demonstrated by 



