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Neuroglia-nuclei occur sparingly in the dotted substance of 
Lumbricus (fig. fig. 'ji,n^n'). 
The Molluscs. 
In Patella we find the dotted substance to have an appearance 
rather different from that of the animals before described. The 
elements of the dotted substance are, here, much smaller, and more 
difficult to trace out than those we have hitherto examined. 
On a careful examination of successfully stained transverse sec- 
tions through the pedal nerve-cord of Patella, it is possible to ob- 
serve a minute reticulation with very small but distinct meshes. It 
is this reticulation which HALLER in the JRhipidoglossa, and Rawitz 
in the Acephales, describe as nervous reticulation. Besides the meshes 
which have extremely slender walls, a great many dark dots are also 
seen. These dots are situated in the walls of the meshes, and 
chiefly in their corners where several walls of various meshes meet. 
It is these dots which Rawitz has described as varicose thickenings 
in the nervous fibrillæ which he supposes to form this reticulation 
in the Acephales. 
On examination of longitudinal sections through the pedal nerve- 
cord, it is seen that the dotted substance has, here, a somewhat 
different appearance. The reticulation seen in transverse sections 
is not present to such extent, on the other hand longitudinally 
running distinctly stained fibrillæ are very prevalent. These fibrillæ 
are extremely slender, and are stained in the same way as the 
reticulation in transverse sections. The intervals between those 
fibrillæ are very small and are of about the same size as the dia- 
meters of the meshes of the reticulation. This indicates that the 
meshes are transsected tubes, and that the longitudinal fibrillæ are 
partly the transsected sheaths of these tubes. It is consequently, in 
so far, a structure somewhat similar to what we have found in 
Lumbricus and Nereis. In longitudinal sections, but especially in 
oblique ones, it is seen that the dark dots visible in transverse sec- 
tions are transsected fibrillæ, chiefly running along the concreting 
edges of the tubes. The question is, now, whether these fibrillæ 
belong to the neuroglia, and are only thickenings in the fibrous sheaths 
of the nerve-tubes, or whether they are real nerve-fibrillæ ^ To decide 
this question, I have examined fresh preparations as well as macerated 
ones, but I must admit, that in this respect I have not till yet succeeded 
■in getting a clear idea of the real relations in the structure of the 
dotted substance of Patella, In fresh isolated preparations of the 
