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memoir on the Archiannelids we may gather that this is the case 
also in those animals (cmfr. p. 57), etc. etcJ) 
Of the results of our researches we may therefore give the 
following summary: 
1) The nerve-tubes of the invertebrated bilaterates consist of an 
external consistent sheath with a viscous contents. 
2) The sheatlis are formed by, or belong to, the connective sub- 
stance extending through the whole nervous system, and which I 
call neuroglia.^) In these sheaths nuclei (neurogiia-nuclei), occur more 
or less sparingly. 
3) The contents of the nerve-tubes consist of primitive tilles, 
which are extremely slender tubes or cylinders, separated from 
each other or rather formed by membranes or sheaths of a firm 
supporting substance, spongioplasm, very much resembling the neu- 
roglia-substance ; these slender cylinders of spongioplasm contain a 
hyaline, viscous substance, hyaloplasm, which is the real nervous 
substance, and which very often is exuded from fresh isolated nerve- 
tubes in form of small hyaline pearls. 
Fibrillæ and fibres, as most writers describe them, do not, con- 
sequently, in my opinion, exist. 
4) A concentration towards a kind of axis is visible in a great 
many largish nerve-tubes of Homarus and Neplirops; this axis may 
be more or less narrow, and consists of a bundle of central primitive 
tubes which have stouter spongioplasmic sheaths and smaller diame- 
ters than the other primitive tubes. A similar concentration in the 
centre of the nerve-tubes can, as a rule, not be observed in the 
other animals examined; only a slight indication of it, I believe to 
have observed in some nerve-tubes of Nereis. 
2. The structure of the ganglion cells, and their processes, 
in invertebrates. 
Homarus vulgaris. 
The contents of the ganglion cells of the lobster consist of 
nucleus and protoplasm enclosed in a thicker or thinner membrane 
or sheath. 
^) In Myzostoma I have previously indicated a similar structure. 
^) In my memoir on Myzostoma (1885) I have called it »the inner neuri- 
lem«, as mentioned before. 
