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roots belonging to the head region and not, as first suggested 
by BALFOUR (1878, p. 205) and afterwards worked out 
especially by FRORIEP and FüRBRINGER, as elements 
of post-cephalic origin that have only secondarily shifted 
forwards into the occipital region, losing their dorsal roots. 
Moreover. ventral roots have since been discovered in 
Amphioxus also (SCHNEIDER, 1879, p. 15), and here evidently 
occur also in the anterior segments which in Craniates 
belong to the head. This renders it probable that in the 
head of the latter ventral roots have been present once 
and have only secondarily been lost when the myotomes 
degenerated. Nevertheless, though BALFOUR's arguments 
appear not to hold water, his opinion quoted above is in 
perfect accordance with the conclusions resulting from my 
theory, as follows from what has been said on the ventral 
roots in the first chapter. BALFOUR, evidently imagined 
the ventral roots to have originated by a process of splitting 
off from the dorsal roots, which, however, seems to me 
to be improbable. 
_ VAN WYHE (1882) has emphasized that the muscles inner- 
vated by the dorsal motor branches of the cranial nerves, 
the constrictores of the gills, though striated and voluntary, 
must yet be considered as visceral muscles, originating from 
the lateral plate and situated in the wall of the gut. The 
nerves supplying them accordingly are to be compared to the 
nerves of the sympathetic system in the trunk. The latter 
come from the sympathetic ganglia which ontogenetically 
are derived from the spinal ganglia. Thus the contrast of the 
‘Cranial ganglia with the latter would be less abrupt than might 
appear at first sight. Only the splitting off of a sympathetic 
ganglion has not occurred. This, however, can also be 
considered as a primitive feature. In Amphioxus the 
separation of a visceral portion from the spinal nerves 
equally fails to find place, the dorsal roots being of mixed 
character. The mixed character of the dorsal roots of the 
head then is no doubt to be considered as a primitive 
feature. 
2. There are segmental communications with the lateral 
organs and, as in Amphioxus, the dorsal roots take their 
path outside the myotomes. Besides the sympathetic elements 
the head ganglia thus also contain the lateral line 
elements which the trunk ganglia have lost, if the concep- 
tion of the ramus lateralis vagi as a collector is right. 
