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contributions to our knowledge of the central fibrous mass of different 
invertebrates (Squilla, Sphæroma, Nephrops), as well as vertebrates. 
He has, very correctly, described it as consisting of connective tissiie 
and nerve-fibres, he has, however, not succeeded in finding the 
real relation between these two substances: »Selon moi, la sub- 
stance grenue-reticulée est formée dun stroma conjonctif et d'un 
réseau nerveux. Le stroma conjonctif réticulé est excessivement fin 
dans les parties centrales du cerveau ; au contraire, dans la périphérie 
des ganglions il est plus grossier et ne différe pas beaucoup de celui 
dont se composent les capsules cellulaires« (1. c. 1881 p. 178). Through 
this reticulation of connective-tissue, extremely slender nervous fibrillæ 
run in all directions, anastomosing with each other and forming another 
reticulation of nervous nature. These fibrillæ are partly derived from 
processes of ganglion cells, and, partly, they are constituents of peri- 
pheric nerve-tubes. He says of them: »ils proviennent des nerfs 
périphériques et des cellules nerveuses et se ramifient en une foule de 
branches grandes et petites qui, les reliant entre eux, forment un 
véritables réseau. « Besides an indirect origin of the nerve-tubes in 
this » réseau «, there exists, however, also a direct origin from gang- 
lion cells: »cependant il est certain que beaucoup de fibres péri- 
phériques proviennent directement du corps des cellules centrales et^ 
dans les plus grandes cellules j'ai remarqué deux prolongements qui 
partent du méme pole; Tun forme directement une fibre nerveuse 
périphérique, Tautre se résout dans le réseau de la substance grenue.<c 
As will be seen, these observations are, in several respects, very 
similar to mine on the nervous system of Myzostoma and of the 
Assidians etc. and, also, to many of those, on various nervous systems^ 
which will be described in this paper. Bellonci has found the same 
» substance grenue-réticulée« in the nervous system of the various 
animals examined by him. 
Arnold Lang has, in his various papers (1879, 1881, 1884)^ 
afforded some valuable additions to our knowledge of the histology 
of the nervous system of the Polyclades, Trematodes etc. In m}^ 
opinion, he has formed a very correct idea of the structure of the 
fibrillar substance in the nerves and ganglia. Of the nerves he says,. 
for instance (1. c. 1884 p. 190): »Das spongiose Aussehen auf dem 
Ouerschnitt kommt dadurch zu Stande, dass der Nerv aus lauter 
kleinen Bålkchen zu bestehen scheint, welche alle miteinander ver- 
bunden sind und welche zahlreiche rundliche, verschieden grosse 
Liicken umschliessen Auf guten Pråparaten aber sind sie 
(i. e. die Liicken) angefiillt von einer feinkornigen blassen Substanz,. 
