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which they accordingly imagine to have closed in the middle by 
coalescence of the opposite borders, leaving only a passage at the 
anterior and at the rear end, the future neurenteric canal and the 
anus, while the rudiment of the tail arises as a double knob at 
the right and the left side of the place of coalescence, these knobs 
fusing afterwards over the middle of the blastopore. Thus ZIeGLER 
(1892) in his little article on the surface-views of Rana-embryos 
writes: “Etwas später sieht man an Stelle des Spaltes eine Rinne, 
welche vorn in den Canalis neurentericus, hinten in die Aftergrube 
übergeht; es sind nämlich jetzt die seitlichen Blastoporuslippen median 
zur Vereinigung gekommen”. In the same way things are represented 
by Hertwic in his Lehrbuch. Already a close examination of surface 
views however teaches us that the anal groove is not at all identical 
with the slit-like blastopore, but that its anterior end coincides with 
the rear end of the latter. The study of median sections excludes 
every possibility of doubt. In the present article I could not insert 
any more some figures of a surface-view and of median sections 
of this stage, in a more detailed account elsewhere I will do so. 
The step to fig. + (plate) seems fairly large, yet this is only apparent. 
Already in fig. 3 we see the cerebral plate curving in. Especially 
notable is the opposition between the praechordal cerebral plate and 
the epichordal medullary plate, which as a matter of fact in this 
stage is no longer a flat plate, but curved into a groove between 
the medullary folds. Fig. 3 however is realized only in one or 
two sections, which are exactly median, to the right or the left 
side immediately one of the medullary folds is intersected, as 
indicated in fig. 3 with a dotted line. A ‘paramedian section in this 
series thus offers a much greater resemblance to fig. 4 where the 
medullary folds have coalesced than the median one of fig. 3. 
Fig. 4 is also of interest in that here apparently for the first time 
the neuropore in Anurans is represented. In his treatise on “Die 
Morphogenie des Centralnervensystems” in Herrwic’s Handbuch, 
Kurrrer (1906) says in regard to Anurans: “Der Neuroporus ist im 
letzten Momente vor seinem Schlusse noch nicht zur Beoachtung 
gekommen”; neither in investigations published since is there anything 
to be found on this subject. Kuprrer accordingly only. represents a 
longitudinal section of a somewhat further advanced stage than in 
my fig. 2 and further stages later than my fig. 4, where the place 
of the neuropore is still recognisable by the presence of a conical 
thickening of the ectoderm or of a recessus neuroporicus in the 
anterior wall of the brain vesicle. It is evident that the curving 
backward of the transverse cerebral fold plays as great a role in 
