274 
DR. H. W. HUBIIECHT. 
Hubrecht’s Researches on the Nervous System of 
Nemertines.^ (With Plate XXIII). 
The above cited paper, which has just been published by 
the Amsterdam Academy of Sciences, and from which we 
have copied figures 1 to 12 on Plate XXIII, gives a detailed 
account of the situation and the structure of the central 
nervous system in the Nemerteaus. After all that has been 
said on this subject in the works and treatises of McIntosh^ 
QuatrefageSj Keferstein, and in a former paper of the same 
author, it would seem superfiuous once more to go over the 
same ground. Only it should be here remembered that the 
histological structure was not, or very insufficiently, con- 
sidered by those authors, whereas, in the present paper, due 
space is allowed to the description of the histological 
details. The minute structure of the so-called side- 
organs ” (McIntosh’s cephalic sacs) is here also for the first 
time minutely entered into. 
A series of experiments is next recorded in favour of the 
author’s hypothesis, that in the Lineidse these '^cephalic sacs” 
with their internal ciliated canal and with the deep longitu- 
dinal slits on each side of the head must be regarded as a 
special apparatus serving for respiratory purposes, the oxygen 
being taken hold of by the haemoglobin contained in the 
nerve-cells belonging to the central nervous apparatus as it 
stretches throughout the whole length of the animal, from 
the head to the tip of the tail. Other arguments in favour 
of this hypothesis are given, some of them derived from the 
phylogenetic, others from the ontogenetic development of 
these organs. 
Finally, the paper discusses an explanation of the origin 
of the dorsal nerve- cord of Vertebrates and the ventral nerve- 
cord of Arthropods and Annelids out of originally paired 
lateral cords. This explanation is suggested by the situation 
of the latter in different genera of Nemerteans, and finds 
itself in harmony with general views which were already 
expressed on former occasions by Gegenbaur, Harting, 
Balfour, and others. Two hitherto unknown facts resulting 
from the author’s investigations are more specially brought 
to bear upon this point ; 1st, the presence in all Hoplone- 
mertini?i% yet examined on this head, of a commissure uniting 
the two lateral nerve-cords and situated above the intestine 
* Dr. H. W. Hubrecht, ‘Zur Anatomie uud Physiologie des Nerven- 
systems der Nemertinen/ Mit Vier 4o Tafeln. ‘ Verhandelingen van de 
Koninklyke Akaderaie van Wetenschappen te Amsterdam/ Dl. 1880. 
