— 94 — 
generally the case, and is more sparingly mixed with nerv^ous ele- 
ments. As will be seen in fig. ii, it has, also, an appearance some- 
what different from the rest of the fibrillar mass, exhibiting, as it 
does, a prominent disposition to form concentric layers or mem- 
branes round the tubes. Between the tubes may also be seen septa 
(flg. II, s), apparently of the same substance, issuing from, or rather 
adhering to, the neurilem-sheath or perineurium, enveloping the 
ventral nerve-cord inside the muscular layer (fig. ii, m). In the 
neuroglia-mass surrounding the three large nerve-tubes nuclei occur 
very often (fig. ii, Jc), they are oblong, have a granular appearance 
and are quite similar to the common neuroglia-nuclei. 
The Mollusca. 
Judging from the latest descriptions of the nervous system ot 
the Molluscs, we should expect, here, to find very extraordinary 
conditions. HALLER assures us that there exists no connective-tissue 
within the nervous system of the more primary Molluscs (Chiton, 
Patella, Rhipidoglossa etc.) and that there really exists no nerve-fibres 
or, as I call it, nerve-tuhes only »Primitivfibrillen« which unite in 
large bundles to form the peripheral nerves. The same statements 
are quite recently made by Rawitz (as mentioned p. 70) as to the 
nervous system of the Acephales; this latter writer seems, however, 
in these as well as other respects, to walk very closely in the 
footsteps of Haller. 
It was therefore with no small interest that I began the investigation 
of this group. I chose Patella vulgata for my purpose, because it 
was on the one hand a large species, and a rather primary mollusc, 
and on the other hand I could get plenty of it, here, in Bergen. 
I must confess, I had some doubt as to the correctness of BÉLA 
Hallers statement that no connective-tissue (i. e. neuroglia) existed, 
and my researches have not at all diminished my doubts; on the con- 
trary, I found a well developed neuroglia, with neuroglia-nuclei of the 
typical form, and sheaths enclosing nerve-tubes. This neuroglia is, 
however, not so well developed as we have seen it in Annelids and 
Crustaceans. It took me some time, therefore, to come to a full 
understanding of the real structure of the nerves and the' nerve-tubes. 
Fresh isolated nerves, as well as nerves macerated in different ways, 
I could, usually, though always with some difficulty, split up into 
fibrillæ, which, however, varied somewhat in size (fig. 17). In 
sections, longitudinal as well as transverse, I came to similar results, 
and could really distinguish longitudinally running darker stained 
fibrillæ, of somewhat varying size; in transverse sections they 
