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sharply defined as on median longitudinal sections. It was then 
seen to be shaped somewhat like a fan. (fig. 2). 
Now the figures drawn by KuPFrer are taken from specimens 
of amphioxus of 4 resp. 2 cM. in length, and in older individuals 
Kuprrer himself could not find the infundibular cavity. ') 
But in examining younger Amphioxus of about 1,5 to 4 c.M. 
in length no trace whatever was to be found of an infundibular 
cavity; in every section-series the differentiated part of the ventral 
wall of the brain could be distinguished with the same clearness 
as in the large specimens I had first studied (fig. 5). 
Fig. 3. 
Ss 
Median section through the head of Amphioxus, 1,9 eM. long. 
In young as well as in older forms there is to be seen a large 
mass of nuclei just behind the differentiated cells, that take a 
deeper stain than the clear cylindrical cells in front of them. When 
the protoplasm of the cylindrical cells is shrunken a little, which 
is not easily to avoid in a material so difficult to fix as Amphi- 
oxus, this mass of nuclei seems to, project into the brain cavity. 
In one section-series, in other respects too less satisfactorily fixed 
than the other specimens I examined, something like this was to 
be seen. Examined under a high power it appeared to be an 
artifact, caused by the shrinking of the long cylindrical cells. 
Different individuals even of the same age show a great amount 
of variation in the median sections through the brain. It is there- 
fore possible that in other forms than I was able to study an 
infundibular cavity as the one described by KUPFFER, may exist. 
I can only say, that in no case I could find it (in specimens of 
about 1,5 c.M. to 4,8 c.M. in length) and therefore must draw the 
conclusion that where it is found, it can be only of a secondary 
importance. In all cases however there appeared the sharply defined 
differentiated part of the epithelium described above. 
1) On a drawing after a cross-section Prof. Kuprrer had the kindness of showing 
to me, the long cylindrical cells were clearly to be seen. 
4G* 
