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to constitute those peripheral nerve-tubes which entirely spring from 
the dotted substance. 
7) The side-branchlets joining those peripheral nerve-tubes which 
,are direct continuations of nervous processes from ganglion cells. 
These side-branchlets are, consequently, partly the same as those 
mentioned in 2. 
We have thus seen that the constituents of the dotted sub- 
stance are tubes, and that these tubes have a rather variable origin. 
What the significance of the dotted substance is, we will in subse- 
quent chapters have the oportunity to examine. 
Nephrops norvegicus. 
In Nephrops the structure and relations of the dotted substance 
is so quite similar to what they are in Homarus, that the above 
■given description will suit in all particulars for both Homarus and 
Nephrops. 
The Nereidæ. 
Amongst the Polychætes, it is chiefly the Nereidæ (especially 
Nereis virens) that I have examined in respect of the structure of 
the dotted substance; I shall therefore in this chapter mention those 
.animals only. 
As the dotted substance of the ventral nerve-cord is the 
simplest, and easiest to investigate, we will confine ourselves to it. 
In the ventral nerve-cord of Nereis the dotted substance has, as 
is well known, a situation and extension very different from what is the 
case in the ventral nerve-cord of Homarus. There are no distinct 
•ganglia, and no distinctly separated longitudinal commissures, the dot- 
ted substance lias, thus, a more uniform extension in two longitudinal 
Tods along the whole nerve-cord. Its composition of tubes is, if 
possible, still more evident than it is in Homarus. In transverse 
^sections of the nerve-cord we find, as before mentioned (vide fig. 14), 
a reticulation with small and large meshes. In longitudinal sections 
we find a longitudinal striation, which shows that the meshes of the 
reticulation, seen in transverse sections, are transsected thick and thin 
longitudinal nerve-tubes. The whole so-called dotted substance of 
the ventral nerve-cord of Nereis consists, thus, principally of longi- 
tudinally running tubes. 
On close examination of sections under high powers of the 
microscope it will, however, be seen that slender tubes pass in 
■all directions between these longitudinal tubes; this is very pro- 
