254 
„FRORIEP, however, declares that all the somites are metotic- 
or occipital and that prootic somites do not exist (l.c.p. 37). 
If former investigators believed that they had observed them, 
this is caused by the erroneous assumption that the auditory 
vesicle has a fixed situation in regard to somites and visceral 
clefts. In reality, however, it wanders backwards during 
pnt 
RE 
Fig. 16 verie of 7 orpedo ocellata, stage 
aud auditory vesicle, Ch rostral end of 
the notochord, ijs occipital somites 
(after FRORIEP, 1902). 
development, while at the same time the foremost somites 
undergo a reduction, being dissolved into mesenchyme. 
At the same time the ‘originally insignificant head-mesoderm 
spreads over the branchial region. It occupies dorsally the 
place left by the dissolved scmites and seizes upon the 
part of the notochord which was formerly flanked by the 
latter and at both sides of which dn heen the parachor- 
dalia, which accordingly belong to the praespinal region, 
The fixed point, from which to Bettien” all these dislocations, 
