PERIPHERAL NERVOUS SYSTEM IN NEMERTINES. 431 
The Peripheral Nervous System in Pal.eo- and Schizo- 
NEMERTiNi^ one of the Layers of the Body- wall. By 
Dr. A. A. W. Hubrecht, of Leyden. With Plates 
XXXII and XXXIII. 
In a paper, which was published in May last, in the 
‘ Verhandelingen van de Koninklyke Akademie van 
Wetenschappen te Amsterdam, vol. xx,’ and which treats of 
the anatomy and physiology of the nervous system of the 
Nemerteans (an abstract of the paper with accompanying 
plate appeared in the July number of this Journal), the 
peripheral nervous system is dealt with very superficially 
only. This was done on purpose. At the time when that 
paper was prepared for the press the results which I had 
arrived at concerning the peripheral nerves in the two sub- 
orders of the Pal^o- and Schizonemertini were so much 
in contradiction with everything hitherto published on the 
subject that I could not venture to publish these results 
before I had been able to convince myself of their trust- 
worthiness in numerous series of preparations, which should 
gradually come under my observation. During the correc- 
tion of the proof-sheets of that paper I was happily surprised 
in obtaining, much sooner than I expected, different sets 
of sections, which, by their superior state of preservation, 
allowed me to settle the point. I could only mention this 
briefly and insufficiently in the explanation of the plate be- 
longing to that article. A more detailed account was at 
the same time promised, and is now embodied in the follow- 
ing pages. 
A. Central Nervous System and Cephalic Nerves, 
The central nervous system of the Nemertines is composed 
of two longitudinal trunks running parallel to each other all 
along the whole length of the body j they are dilated ante- 
riorly into a very simple or a more complicated pair of brain- 
lobes, situated above the alimentary canal (often in front of 
the mouth), and united together by a ventral and a dorsal 
commissure, the latter always thinner than the former. 
Posteriorly these longitudinal trunks either terminate very 
close to the end of the body, or they are again united by a 
third commissure, which, like the brain, passes above the 
alimentary tract in the anal region. The whole of the cen- 
tral nervous system (“ marrow-trunks ” and brain-lobes) 
