— 128 — 
are of real nervous nature, and are not simply fibres belonging to the 
connective substance, neuroglia, is not, I think, open to argument. 
To clecide the above question is not easy. As before mentioned, 
it has not been possible to detect any structure inside the sheaths 
of the primitive tubes, neither in the nerve-tubes nor in the dotted 
substance. In spite of this a structure may of course be present; 
the primitive tubes are already so very minute that even our present 
powers of the microscope, thougli high, would not readily sufhce to 
exhibit such a structure of small tubes or fibrillæ inside them. We, 
therefore, at present, stand, here, before a terra incognita, and must 
content ourselves with suppositions, which we will, however, leave 
the reader to form for himself. What we know is that, these 
fibrillæ spring from subdivisions of nerv^e-tubes or primitive tubes 
— or they are given off, from them, in form of slender lateral 
branchlets, and it is then, perhaps, most reasonable to assume that 
they arise only by a subdivision of primitive tubes. 
As to their course in the dotted substance, I will expressly 
say that, I have never succeeded in observing these fibrillæ to form 
a reticulation ivith real meshes, neither have I seen them anastomose 
with each other, They frequently exhibit, in sections, an extremely 
complicated course with a great many subdivisions and branches, 
but in my preparations they always avoid union with each other. 
They form, consequently, a kind of loose plaiting or web and not a 
reticulation as most authors describe. They pass along the walls 
between the thicker tubes of the dotted substance. 
What previous authors have described as nervous reticulation 
in Homarus, as well as other invertebrates, is, as mentioned above, 
the transsected tubes, primitive tubes and nerve-tubes, forming the 
dotted substance, the sheaths of which tubes, in sections, give the 
appearance of a reticulation. Leydig describes, as mentioned p. 60, 
a sponge-work (»Schwammwerk«, »Balkenwerk«) in the dotted sub- 
stance, which sponge-work he supposes to be of the nature ot a 
support; the real nervous substance, hyaloplasm, is diffusively ex- 
tended in the cavities of this sponge-work. As may be seen from 
^) Leydig does not exactly state what he supposes to be the origiu of this 
reticulation. In «Zelle und Gewebe« 1885 p. 173 — 174 he only speaks of the 
dotted substance as containing a «protoplasmatisches Netz- oder richtiger Schwamm- 
werk«f. Of this «Schwammwerk* or »Balkenwerk« he says : »avo nun Nervenur- 
sprunge gesetzt sind ordnet sich das Balkenwerk zu Långsstreifen, die zwischen 
sich die homogene Grundsubstanz ebenso aufnehmen, als es in dem sich durch- 
kreuzenden Maschenwerk geschehen war.« In another place he says, however, that 
the dotted substance ^>entsteht durch fortgesetzte Theilung und netzige Auflosuag 
der Fortzatze der Ganglienkugeln, genauer gesagt, ihres Spongiplasma« (1. cp. 187). 
