1 
— 54 — 
richtung der Thiere gefiihrt sind, dasselbe spongiose Gewebe, wie 
in den Nerven auf Ouerschnitten. Bei beiden sehen wir auf Flachen- 
schnitten dasselbe System mit einander verbundener Rohren und 
in diesen Rohren liegen bei beiden gleichartige Ganglienzellen.« ^) 
In the »Stiitzgewebe« Lang even describes what he calls: 
„Faser]ierne'' (vide 1. c. 1879 p. 485 and Taf. XV, fig. 5 and Taf. 
XVI, fig. 7, fk.); they have completely the appearance of neuroglia- 
cells. Although Lang does not say anything regarding his view of 
the nature of these nuclei, I do not think there can be any doubt 
of their real neuroglia-nature (vide also Monograph 1884, Taf. 32, 
fig. 9, d, e, f, g, and also Taf. 31, fig. 6, g z 3, g z 4). Lang even 
describes small nuclei adhering to the processes of the ganglion cells, 
(»Auch der kleinen, den Auslåufern der Ganglienzellen anliegenden 
Kerne mussen wir, als allgemein vorkommend, Erwahnung thun.« 
Mon. 1884 p. 183, Taf 32, fig. 9, a). These nuclei have, also, quite 
the appearance of those belonging to the neuroglia, as will be seen 
from Lang's illustrations. It is, consequently, a situating of neuroglia- 
cells quite similar to what I have previously described in Myzostoma^ 
and to what will be described, particularly of MoUuscs, in this paper. 
In the Trematodes there must, in his opinion, be a direct origin 
of the nerve-tubes from ganglion cells, so far as I understand him. In 
his description of their brain he says, for instance: » Auf liickenlosen 
Serien von Quer-, Langs- und Flåchenschnitten ist es moglich, alle 
Einzelheiten des Faserverlaufs zu erkennen und die Fortsatze wenigstens 
der grossern Ganglienzellen bis in die Nerven hinein zu verfolgen.«2) 
Whether the nerve-tubes of the Polyclades have a direct origin in 
ganglion cells of the central nervous system, or an origin in the 
central fibrillar substance, he does not mention, and neither does 
he give any distinct description of the dotted substance in these 
animals besides what is above quoted (vide p. 53). The central 
part of the brain, he says, consists »aus einer sich sehr schwach 
fårbenden, ausserordentlich feinfaserigen Substanz, in deren Inneren 
weder Kerne noch Ganglienzellen vorkommen.« From this descrip- 
tion it is, however, evident that we have a similar structure of the 
^) Regarding these cells situated in the nerve-tubes, vide foot note 2. 
2) In the peripheral nerves, he describes nerve-tubes wich are direct processes 
of ganglion cells situated in the nerves. The nerves of the Trematodes, he says, 
(1. c. 1 881 p. 37) consist «zweitens aus der Nervenfaser, die, in diesen Røhren ein- 
geschlossen, die Fortsatze der ebenfalls in ihnen liegenden Ganglienzellen darstellt.<f 
As I have not examined the Trematodes, I can, of course, fonn no opinion of 
the correctness of this statement. 
