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‘my theory and, at the same time, into better agreement 
‚with the facts. fFesides the ventral ganglia we find, as 
anentioned above, in Annelids still another group of segment- 
al ganglia, the lateral or the parapodial ganglia. Now we 
have traced back already the spinal ganglia of Vertebrates 
to the ganglia of the ventral nerve-chain in Annelids. What 
are we to think of the lateral ganglia of the latter in 
Vertebrates? If they are found here, Il think it is only in 
the branchial region. 
Dermatogenetice part of the cranial ganglia. — In the year 
1885 it was found simultaneously, but independently, by 
BEARD in Elasmobranchs, by SPENCER in Amphibians and 
by FRORIEP in Mammals, that several of the cranial ganglia 
do not originate, like the spinal ganglia, exclusively from 
the neural ridge, but that also the lateral epidermis of the 
‘head plays here a considerable part. The ganglia referred 
to are in fact those of the N. frigemenius, the acustico-facialis, 
the glossopharyngeus and the vagus. The first rudiments 
of these ganglia, produced by the neural crest, grow 
downwards between the ectoderm and the outer side of the 
myotom, and in Ichthyopsids each fuse with the ectoderm 
at two places, one above the other: a lateral one, some- 
what on the level of the notochord, and an epibranchial 
one, just above the gill-slits. At the point of fusion with 
the epidermis, thickenings of the latter, placodes, arise, 
which look much like sense-organs. The corresponding 
part of the lateral line, which on the head deveiops earlier 
than on the trunk, originates afterwards from the lateral 
series. At the placodes a proliferation of the epidermis 
sets in; epidermal cells, dividing actively, are given off 
to the inside, forming a ganglion. At their first appearance 
these dermatogenetic placode ganglia in some cases are 
quite independent from the centrogenetic spinal ganglia, and 
in the frog, according to BEARD (1888b, p. 900), they sepa- 
rate from the epidermis before the spinat ganglia, growing 
out downwards, have reached them. FRORIEP (1885, p. 37) 
and BEARD (1885, p. 221) have suggested independently, 
that the placodes represent rudiments of segmental sense 
organs, belonging to the lateral line. Much can be said 
then for the supposition, that the lateral head-ganglia corres- 
pond to the lateral ganglia of Annelids, the ganglia of the 
lateral sense-organs. Soon afterwards the dermatogenetic 
ganglion fuses intimately with the centrogenetic one, SO 
