NERVES WITHOUT FIBRES. 393 



sion, or the result of disintegration in the nerve itself ; 

 but having examined both fresh and prepared speci- 

 mens, in great quantities, I aflSrm, that in the genera 

 Doris^ Pleurobranchus, Aplysia, Solen, and Limax, 

 the nerves are for the most part totally destitute of 

 fibres.* 



Within the investing sheath of areolar tissue f is 

 contained a mass of granules, cell nuclei, and occa- 

 sional cells large and small, but not one primitive 

 nerve-fibre. If we compare the structure of the nerves 

 in the Doris with that in the garden Snail, we shall 

 immediately perceive the difference, the latter animal 

 having distinctly fibrillated nerves, the former nothing 

 but amorphous nerve-substance. At first it occurred 



* Dr Inman, of Liverpool, infoi-ms me, while these sheets are pass- 

 ing through the press, that he has examined the nervous system of 

 three very fine specimens of Dendronotus arhorescens in which he finds 

 precisely the disposition I have described : " The nervous masses were 

 made up of very large cells, ilii inch in diameter, full of granular mat- 

 ter, and surrounded by a thick coat of granular material of a brownish 

 colour. These were most numerous in the four large ganglia, but were 

 found sparingly in the main nen^ous trunks. Some cells or vesicles 

 were much smaller than others, the smallest about jio of an inch. 

 The nervous trunks were fiUed with granular matter, in which no ap- 

 pearance of fibrillation could be traced, but on squeezing out the 

 neurine it was found that there was an abundant supply of vesicles of 

 various sizes, as well as of granular matter. In one main tube at some 

 distance from the ganglia there was a faint appearance of fibres which 

 were very small in length and breadth, and quite solid." This last 

 fact is very interesting, and agrees with what I have noted fm-ther on 

 of the dragon-fly larvae. 



"t* It may not be unnecessary to warn the amateur who may verify 

 these observations, not to confound the fibres of the investing sheath 

 with nerve-fibres. 



