201 
daeum, and in thís way the latter might have been taken up into 
the nervous system so as to form part of it. With such a sup- 
position the facts of ontogeny are in harmony. As Hs (1886) 
first observed in the human embryo, the dorsal nerve roots are 
produced exclusively by the spinal ganglia. From these grow 
out the nerve-fibres which constitute the peripheral part of 
the dorsal nerve, whereas on the other side they grow out into 
the medullary tube, thus constituting the root of the dorsal 
nerve. With this result, those obtained experimentally 
by cutting off the dorsal nerve under and above the ganglion 
and studying the degeneration of the nerve fibres, as shown 
first by WALLER (1852) and afterwards by many others, 
are in harmony. It can be demonstrated in this way that 
the ganglion is the trophic centre for the whole dorsal root. 
Finally it may be observed that the sympathetic nervous 
system with its ganglia is a derivâtive of the spinal ganglia. 
Spinal nerves. —lf now the assumption made above is 
correct the dorsal component of the spinal nerves issuing 
from the spinal ganglion must be compared with the seg- 
mental nerves radiating from the ventral ganglion of the 
Annelid. These latter nerves, however, are of mixed motor 
and sensory function, and thus we are led to a conclusion, 
put forward for Vertebrates by FRANCIS BALFOUR as early 
as 1878. BALFOUR did not observe ventral roots in Amphioxus 
and the dorsal nerves are of a mixed sensory and motor 
nature. The same applies to the dorsal nerves of the head 
of Craniotes, where also BALFOUR did not recognize any 
ventral roots. Thus he expressed as his opinon (l.c. p. 193): 
“that primitively the cranio-spinal nerves of Vertebrates 
were nerves of mixed function with one root only, and 
that root a dorsal one, and that the present anterior or 
ventral root is a secondary acquisition” (cf. also 1881, II, 
Pp. The original condition is found still in Amphioxus 
and in the head of Craniates 
To this conclusion VAN WH (1882, p. 40) has objected : 
1°. that soon afterwards ventral roots have been dis- 
covered in Amphioxus (SCHNEIDER, 1879, p. 15), 
2°. that in the trunk the dorsal root originates indepen- 
dently of the ventral one. VAN WYHE here evidently 
assumes that in BALFOUR's ben the ventral nerves are 
to be derived from the dorsal one 
3°, that BALFOUR did not cous the oculomotorius, 
trochlearis and abducens as ventral roots, as proposed by 
