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grey substance and just to the periphery of the white substance 
(to the sheath of connective tissue). They seem to compose a signi- 
ficant constituant of the white substance. Subsequently they will be 
more circumstantially described. 
The structiir e of the nerve-ttihes is the same, in Myxine, 
as in the other animals examined. The nerve-tubes consist of a 
distinct external sheath, and a contents containing spongioplasm and 
hyaloplasm. The external sheaths are rather thin (vide fig. loo). 
The contents of the nerve-tubes consist of primitive tubes. In 
the large nerve-tubes (Muller's nerve-tubes), the primitive tubes are 
very distinctly seen (vide fig. lOO, Int).^) Upon the whole, it is striking 
how very much these MULLERs nerve-tubes resemble the large nerve- 
tubes of the lobster; in Myxine I have even observed a tendency 
to the formation of an axis along the centre of some larg tubes 
(vide fig. lOO, Inf) somewhat similar to what is described of the large 
nerve-tubes of the lobster (vide p. 87). 
Medullated nerve-tub es are not observed in the spinal cord 
of Myxine. 
The ganglion cells are situated in the grey substance; they 
are, as a rule, multipolar, have always one nervous process each, 
and generally several protoplasmic ones. 
The protoplasm of the ganglion cells has, in sections, always a 
minute reticular appearance, with spongioplasmic meshes containing 
a less-staining substance; the meshes are, to a great extent, produ- 
^) I think it is very strange that previous authors have not seen the compo- 
sition of primitive tubes in the large nerve-tubes of the spinal cord of the fishes. 
In his description of the large nerve-tubes in medulla oblongata of Lophius, 
Fritsch says (1. c. 1886, p. 22): »Der Faserlangsschnitt zeigt, dass die Fibrillen 
nicht regelmassig parallel angeordnet sind, sondern sich vielfach durchflechten . . . .« 
It is obvious, in my opinion, that Fritsch has seen the spongioplasmic walls of 
the transsected primitive tubes and has called them »Fibrillen«. 
Stilling has long time ago (1. c. 1855) decribed the contents of the nerve- 
tubes of the Vertebrata as consisting of slender tubes; he said himself in his 
paper that there would likely go a long time before anybody could state the cor- 
rectness of his observations, as it was only by help of new and very high powers 
of the microscope he had been able to obtain his results. Indeed, there has gone 
a long time; no other writer has since been able to see Stillingas »Elementar- 
nervenrorchen». His observations were made too early. They were of cource, 
imperfect, as he had not the same lenses and modes of investigation as we 
have at precent; a great deal of v^hat he has seen, has been artificial products 
(e. g. his description of the myeline of the medullated nerve-tubes) but he has 
said that the cylinder-axis consist of slender „Elementarrdrchen" and in this 
point I do entirely agree with him. 
