90 
F. M. BALFOUR. 
On the Spinal Nerves <?/■ Amphioxus. By F. M. Balfour, 
M.A., E.E.S. Fellow of Trinity College, Cambridge. 
In an interesting memoir devoted to the elucidation of a 
series of points in the anatomy and development of the Verte- 
brata, SchneideF has described what he believes to be motor 
nerves in Amphioxus, which spring from the anterior side of the 
spinal cord. According to Schneider these nerves have been 
overlooked by all previous observers except Stieda. * 
P myself attempted to show some time ago that anterior 
roots were absent in Amphioxus ; and in some speculations on the 
cranial nerves, I employed this peculiarity of the nervous system 
of Amphioxus to support a view that Yertebrata were primitively 
provided only with nerves of mixed function springing from the 
posterior side of the spinal cord. Under these circumstances, 
Schneider’s statement naturally attracted my attention, and I 
have made some efforts to satisfy myself as to its accuracy. The 
nerves, as he describes them, are very peculiar. They arise 
from a number of distinct roots in the hinder third of each 
segment. They form a flat bundle, of which part passes up- 
wards and part downwards. When they meet the muscles they 
bend backwards, and fuse with the free borders of the muscle- 
plates. The fibres, which at first sight appear to form the nerve, 
are, however, transversely striated, and are regarded by Schneider 
as muscles ; and he holds that each muscle-plate sends a process 
to the edge of the spinal cord, which there receives its innerva- 
tion. A considerable body of evidence is requisite to justify a 
belief in the existence of such very extraordinary and un- 
paralleled motor nerves; and for my part I cannot say that 
Schneider’s observations are convincing to me. I have attempted 
to repeat his observations, employing the methods he describes. 
In the first place, he states that by isolating the spinal cord 
by boiling in acetic acid, the anterior roots may be brought into 
view as numerous conical processes of the spinal cord in each 
segment. I find by treating the spinal cord in this way, that 
processes more or less similar, but more irregular than those 
which he figures, are occasionally present ; but I cannot per- 
suade myself that they are anything but parts of the sheath 
of the spinal cord which is not completely dissolved by treatment 
with acetic acid. By treatment with nitric acid no stick processes 
1 ‘Beitrage z. Anat. u. Entwick. d. Wirbelthiere/ Berlin, 1879. 
2 “ On the Spinal Nerves of Amphioxus,” ' Journ. of Anat. and Pliys. ’ 
vol. X, 1870. 
