— 92 — 
nt represents smaller surrounding nerve-tubes. As will be seen, 
there is, in these tubes, a longitudinal striation quite similar to what 
we already have experienced in Homarus. 
The nerve-tubes of the peripheral nerves have quite a similar 
structure to those of the ventral nerve-cord. 
The sheaths of the nerve-tuhes are formed by the neuroglia, 
in the same way as they are in Homarus (cmfr. fig. lo); they are, 
however, not so stout, and nuclei occur very sparingly in them. 
Iiumbricus agricola. 
In Lumbricus, the nerve-tubes in the ventral nerve-cord have a 
more uniform and relatively smaller size (the three »gigantic nerve- 
tubes « excepted [fig. ii, t,t,ti]) than they have in the ventral nerve- 
cord of the Polychætes exarained; the nerve-tubes have, however, 
a quite similar structure, their contents being composed of the same 
elementary constituents, viz. the primitive tubes, which certainly have 
a small diameter, but are, in the small nerve-tubes, only present in 
limited number; in some cases nerve-tubes consist of apparently 
only one primitive tube; it is consequently somewhat similar to what 
is described in Nereis and Crustaceans. 
The nerve-tubes have neuroglia-sheaths which are very prominent 
in osmic-hæmatoxylin preparations, vide fig. ii, nt. 
The nerve-tubes of the peripheral nerves have a quite similar 
structure to those of the ventral nerve-cord. 
In the ventral nerve-cord of Lumbricus, there are, as is well 
known, three large tubes running, dorsally, through the whole length 
of the nerve-cord. These tubes, which are generally called »Clapa- 
RÉDEs gigantic nerve-fibres«, have given rise to much dispute and in 
the views of the various writers very different functions have been 
attributed to them. Some writers have called them supporting rods, 
the function of which is to give support and rigidity to the ventral 
nerve-cord under the many movements of the animal; that is, for 
instance, Vejdovskys view; other writers, again, consider them as 
homologous with the corda spinalis of the vertebrates; some writers 
call them vessels, etc. etc, and finally a great many writers call 
them nerve-tubes. Lately, Leydig has published a paper on this 
subject (1. c. 1886) in which he very emphatically maintains their 
exclusively nervous nature. 
After having examined their structure, I do not think there can 
be any doubt that Leydig is right, and that Vejdovsky, who ex- 
presses himself with so much self-confidence, is entirely wrong. It 
was indeed to be hoped that those organs might at last enjoy that 
