50 . A, A. W. HUBRECHT. 
conclusions concerning the origin of the vascular system in 
the Amphibia are Goette (75) and Schwink (’91). Both are 
convinced that all blood-cells are derived from the endoderm, 
as also the vessels. Brachet points out, however, that the 
stages on which Schwink bases his conclusions are already 
too far advanced. 
It is important that Brachet, repeating Corning’s (799) 
observations, finds that in front of the notochord’s anterior 
end the median protochordal-plate-material differentiates 
from behind forwards in this sense that mesoblast is seen to 
become isolated and to form a thin layer made up out of one 
or two layers of cells that are interposed between the ento- 
derm and the lower brain wall. In the beginning he finds 
that the anterior end of the notochord reaches into this 
median mesoblastic band... Soon, however, it 1s separated out 
of it and the anterior extremity of the notochord becomes 
quite free. Later yet the median mesoblastic band thins out, 
breaks up and ultimately disappears, or is reduced to a few 
sparse cells that are distributed at random. ‘I'he endoderm 
of the roof of the digestive tube is then closely pressed 
against the lower wall of the brain. 
This would, ceteris paribus, also apply to the mammalia. 
The next point we have to consider concerns the fusion 
described for mammalia by myself (90) and others, and for 
Hypogeophis by Brauer of what we have called the proto- 
chordal plate with the protochordal wedge. Neither amongst 
Brachet’s figures for Axolotl, nor among those for the frog, 
are the phenomena so self-evident as they were for Brauer’s 
Hypogeophis. Still if we consider Brachet’s figures of Axolotl 
and those for the frog no objection can reasonably be raised 
against my comparing the region which in all these figures I 
indicate by Pp. with that same region in Hypogeophis and in 
mammals. The fusion with the ectoblastic proliferation that 
is the protochordal wedge—although Brachet does not look 
upon it in that light—is inaugurated for Axolotl in Brachet’s 
(03) Figs. 4 and 5; for Rana in Fig. 79, here given. The 
ectodermal proliferation indicated as protochordal wedge is 
