NEllVES WITHOUT FIBRES. 375 



I incline to think that in the Doris no fibre can be found 

 anywhere ; but as all such negatives are perilous, I simply 

 state what I have seen, namely, that for the most part the 

 nerves are fibreless.* 



Within the investing sheath of areolar tissue -|- is con- 

 tained a mass of granules, cell nuclei, and occasional 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 SnaU, we shall immediately perceive the dif- 

 ference, the latter animal having distinctly fibrillated nerves, 

 the former nothing but amorphous nerve- sub stance. At first 

 it occurred to me that the granular structure might be 

 peculiar to the molluscs without shells ; but the bivalve Solen 

 and the Aplysia contradict such a suggestion. 



Again, in the brains of several Tritons, or "Water- Newts, I 

 could find no fibres ; none in that of a young Frog ; none in 

 that of an adult Toad ; none in that of the adult Pipefish 



* Dr Inman, of Liverpool, informs me, while these sheets are passing through 

 the press, that he has examined the nciTous system of three very fine speci- 

 mens of Dendronotns arhorescens in which he finds precisely the disposition I 

 have described : "The nervous masses wore made up of very largo cells, ijfi 

 inch in diameter, full of granular matter, 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 sjjaringly in the main nervous trunks. Some 

 cells or vesicles were much smaller than others, the smallest about jIb of an 

 inch. The nervous trunks were filled with granular matter, in which no appear- 

 ance 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 g-anglia 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 further on of the dragon-fly larvto. 



f It may not be unnecessary to warn the amateur who may verify these obser- 

 vations, not to confound the fibres of the investing sheath with nerve-fibres. 



