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In the Annelids we find a structure of the nerve-tubes very 
similar to what is described in Homarus. 
Poiychætes. 
As representative of the Poiychætes I have examined several 
spedes of Nereis (N, virens, N. pelagica and others) and also, 
occasionally, Nephtys, Leanira etc. and can only say that, in them 
all, I have found the same structure of the nerve-tubes repeating itself. 
In the Nereidæ, to which I have especially paid attention, we 
find nerve-tubes of every thickness, ranging from the two gigantic 
nerve-tubes running along the centre of the ventral nerve-cord (vide 
fig. 14 and fig. 10) down to nerve-tubes consisting of only one pri- 
mitive tube, like what is described in Homarus. ^) 
The minute structure is, of course, easiest to study in the larger 
nerve-tubes. If we examine them under high powers of the micro- 
scope, in good preparations, 2) we find that quite similar primitive 
tubes constitute their contents, in the same way as described in re- 
spect of the nerve-tubes of Homarus. The difierentiation in primi- 
tive tubes is, however, not so distinctly marked nor so easily seen 
as it is in Homarus, perhaps, partly, because the primitive tubes 
have a smaller diameter,^) partly, because their spongioplasmic 
sheaths or membranes are thinner and less distinct. In fact, it often 
requires the best lenses, and very carefully prepared preparations, 
to see any structure in the contents, and this is evidently the reason 
why so many authors have not understood these structures, and 
have supposed these large nervetubes to be lymphoid vessels etc. 
Of a concentration towards an axis, there are only very slight indi- 
cations in some rather slender nerve-tubes. The large nerve-tubes 
(»gigantic fibres«) have always primitive tubes, only slightly marked, 
and of the same size and appearance throughout. Fig. 10 represents 
the central part af a transverse section through the ventral nerve- 
cord, where one of the two central largest nerve-tubes [i) (of the 
other only a small part is seen), also some more ventrally situated, 
not so large nerve-tubes {ti,t2,t^) and a great deal of the surround- 
ing small nerve-tubes (nt) are seen. Fig. 9, b represents a longi- 
tudinal section of one of the largish nerve-tubes (cmfr. fig. 10, ^2); 
^) In my preparations I have found nerve-tubes with diameters measuring 
from .030 Mm. down to .0018 Mm. 
^) For this purpose the same method of fixing etc. can be recommended as 
we have recommended for the neve-tubes of Homarus (vide p. 85). 
^) In my preparations I have generally found the diameter of the primitive 
tubes to be about .0012 Mm. or less. 
