— 70 — 
scription quite similar to that of Haller. It is a anastomotic net- 
work of slender fibrillæ, which is diffusively extended through the 
whole dotted substance, and which is formed by the »Markfortsåtze« 
of the ganglion cells, as also by the »Schaltzellen«, mentioned above. 
The only difference between Rawitzs and Hallers descriptions is: 
that Rawitz ascribes to his »Nervennetz« numerous »Varikositåten«, 
whilst Haller does not mention anything similar; they occur at the 
points where the hbres forming the meshes unite; they appear »im 
mikroskopischen Bilde als dunkle Punkte« ; and they are real vari- 
oceles and not merely optic products (1. c. p. 429). Besides this 
»Nervennetz« and the »nervenmarkåhnliche Substanz« there is, in 
the »Marksubstanz«, a third constituent, i. e. slender fibrillæ which, 
in macerated preparations, may be isolated for long distances, and 
which are also varicose. »Sie sind ausserordentlich schmal aber 
nicht smaler als die peripheren Fibrillen Sie steilen das Pro- 
dukt des centralen Netzes dar, aus dem sie sich . . , durch Ver- 
schmelzung von 2 oder hochstens 3 Netzfibrillen entwickeln.« . . . 
»Die Fasern selber treten durch die Maschen des Netzes hindurch, 
um vom ihrem Bildungsort zur Peripherie zu gelangen und werden 
wohl durch die markåhnliche Substanz von den Fibrillen des Netzes 
isolirt.« Strange to say, Rawitz supposes, here, the importance 
of this substance to be only isolation, whilst the substance he 
found in the ganglion cells, and which he suposes to be similar to 
this one, ought, in his opinion, to be considered as the real nervous 
substance strictly speaking, and the reticulation in the cells a sup- 
porting substance; that is consequently quite a contrary view. 
According to Rawitz, connective-tissue occurs neither in the 
central nervous system of the Acephales nor in their nerves inside 
the outer sheaths, and in spite of this statement he describes cells, 
occuring in the nerves as well as in the central nervous system, so 
strikingly similar to those of the neiiroglia, or inner neurilem, that 
I do not think there can be much doubt about their identity (e. g. 
comfr. his »Schaltzellen«, »geschwanzte Kerne«, round nuclei and 
oblong nuclei in the nerves etc). 
Regarding the structure of the nerves of the Acephales he says 
that »die Nervenfasern einfach ein primares Bundel von Axenfibrillen 
sind.« This is, in my opinion, a mistake, in which he, however, 
agrees with HALLER and other writers. 
Rawitz wonders that HALLER did not know the paper by 
Bellonci on the »Tectum opticum der Knochenfische« (Zeitschr. f. 
