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neurotroch of Annelids and the medullary tube of Verte- 
brates, and the posterior part of the circular rudiment of 
the neural plate surrounding the wide open blastopore 
might be compared with it. In Amniotes the primitive 
streak, along which the blastopore moves backwards, is 
then distantly comparable to the neurotroch, since here too 
we have to deal with the coalesced lateral borders of the 
blastopore. 
In fig. 362 has been indicated how in Craniates the 
praechordal cerebral plate (A. pl.) is added to the epichordal 
neural plate (m. pl), while in Acrania the condition shown 
in fig. 36/ persists. 
Summary. — From the foregoing considerations on the 
Ea of Chordates the following conclusions result: 
All that sinks beneath the surface represents the pri- 
mary endoderm or hypoblast, and that which remains 
at the surface is the ectoderm or epiblast (contra 
LWOFF). 
2. That which formerly has been always considered 
as the blastopore is indeed the blastopore, not a 
“notopore” (HUBRECHT) or a “somatopore” (DE LANGE) 
which are only a very little part or the rest of the 
blastopore. 
3. The phenomena occuring during the contraction of the 
blastopore border must be called gastrulation, not 
“notogenesis” (HUBRECHT) or “somatogenesis” (DE 
LANGE), following after the gastrulation. Truly, during 
gastrulation the embryo of Amphioxus assumes an oblong 
shape, which proves that at this moment the growing out 
of the segmented soma has already begun, as is shown also 
by the circumstance that only a little later a whole series of 
mesodermic segments appears. If we call the growing 
out of the segmented soma in Annelids “somatogenesis’, 
then we must say that in Vertebrates the “somatogenesis” 
interferes with the kds and does not come 
after it. In this sense 1 propose to use the term “soma- 
togenesis’’ in future. ASSHETON (1894) was right in 
distinguishing two growing processes of which the latter, 
called notogenesis by HUBRECHT and somatogenesis 
by DE LANGE, is connected with the longitudinal 
growth of the embryo, but he did not make out the 
correct relation between the two and the way in which 
they interfere mutually. 
