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contrary on the outer side. After FRORIEP (1901), who, as 
we have seen, is inclined to emphasize the contrast between 
the “praespinal”’ or “cerebral” part of the head and the 
rest of the body, we have to do here with two different 
neural crests, which in the occipital region run along each 
other for some distance. DOHRN (1902) however does not 
admit thís contrast and GUTHKE (1906) finds that the 
spinal ganglion crest behind the last gill-slit crosses the 
eighth segment, thus passing from the inner side of the 
somites to the outer side, where the head ganglia are found. 
According to ZIEGLER (1908) the lateral situation of the 
head ganglia stands “wahrscheinlich in Beziehung zu der 
Placodenbildung und ist demnach die Folge der Ausb.Idung 
der eigenartigen Sinnesorgane, als deren palingenetische 
Reste jetzt die Placoden auftreten”. Finally GAST (1909, p. 
375) believes, that a double ridge is found not only in the 
region where cephalic and trunk neural crest, according 
to FRORIEP, run for some distance parallel to each other, 
but that this double nature is characteristic of the whole 
head and trunk. According to the conclusions arrived at 
by us regarding the relations between spinal and lateral 
ganglia, the lateral situation, if ZIEGLER's view were right, 
would have been the primitive one also for the spinal 
ganglia, and the present situation, on the inner side of the 
somites, ought to be considered as secondarily acquired 
after the loss of the segmental communications of the 
Spinal with the lateral ganglia. A last trace of this might 
be found in GAST's observation of the double nature 
of the trunk neural crest. But here we may stop our 
speculations in this direction, in which we may, perhaps, 
have gone too far already. 
Eye-muscle nerves.—Finally the oculomotorius, trochlearis 
and abducens have been compared by VAN WYHE (1882) 
to the ventral roots in the trunk region. The oculo- 
motorius is considered as the ventral root of the first or 
praemandibular segment and innervates the eye-muscles 
derived from it, the trochlearis as the ventral root belong- 
ing to the second or mandibular segment, while the. 
abducens in counted as belonging to the third or hyoid 
segment. 
We will revert later to the question whether a ventral 
root belongs to the following segments (ventral vagus roots 
of GEGENBAUR, hypoglossus in Amniotes!). Thus the number 
