Description of my investigations. 
i. The structure of the nerve-tubes in invertebrates. 
Homarus vulgaris. 
The nerve-tubes of the lobster (Homarus vulgaris) consist, as is 
well known, of an external sheath, with nuclei, and a viscous con- 
tents, They have a rather homogeneous and refractive appearance 
with doubly marked outlines when they are examined in the live-state 
under low powers of the microscope. ^) On application of higher 
powers, a longitudinal striation, not very prominent but still quite 
distinct, is seen to form an axis in the centre of some large nerve- 
tubes (vide Pl. II, fig. 12, A Sz: B). This striated axis is, in some 
tubes, very narrow (fig. 12, A) and in the rest of the tube-contents 
no striation is visible, but only a few lines close to the axis. In 
other tubes the striated axis is broader, and more numerous lines 
are seen in the contents round it. In some tubes the striated axis 
is even very broad (fig. 12, B), and lines are visible almost through 
the whole contents except in the peripheral layers ; they do not usually 
occur there or are, at all events, very rare. Upon a careful exa- 
mination of several preparations it is, in fact, possible to find every 
stage of striation, from tubes with a striation through the whole mesial 
parts of their contents, to tubes with a very narrow striated axis in 
their centre, in all these tubes it is, however, possible to observe a 
concentration of the striation towards the centre of the tubes, in such 
1) For examination of the tubes in the live-state, I think it is best to take long 
pieces of the nerves or commissures with their sheaths, "as intact as possible, and 
examine them quickly in the blood of the animal; a method which is especially 
recommended by Freud (1. c. 1882). The oesophageal commissures I found to be 
very suitable for the purpose as they are not too thick and can be very quickly 
extricated. I have, of course, also isolated the tubes in the blood of the animal, 
and think this method to be very good, for some purposes, when it is quickly 
performed. 
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