Median section through the head of Amphioxus lanceolatus 4,6 cM. long. 
Inf. 0. = differentiated epithelium. Pv. = pigmented spot. 
Ch. = chorda. g.e. = large ganglion-cells. 
in the region of the infundibalar cavity of KupprFER’s figure, a 
sharply marked off part of the floor of the brain cavity (Inf. 0.) was to be 
seen, consisting of long cylindrical cells, the whole in the form of a 
cup. The inner boundary of the brain cavity did not show even the 
faintest hollowing out, but only went sloping down gradually until 
somewhat behind the eye-spot. The sharply defined differentiated 
part of the floor projected somewhat (but only very little) into the 
brain cavity. It consisted of very long cylindrical cells with a very 
clear protoplasm and a small round nucleus lying at the base of 
the cell. On their free surface these cells carried thin but long 
cilia, bent backwards and forming a bundle of thin fibres that could 
be traced as far as the beginning of the central canal. Each cell 
seemed to be provided with one hair. 
Fig. 2. In sections stained with chloride of 
gold (after Apathy) in each cell was to 
be seen a rather thick *Neurofibrille”, 
entering the cell at its base, forming a 
network round the nucleus and finally 
ascending through the cell and ending 
just beneath the place of attachment of 
the cilia with a small knob, lying close 
against the intracellular prolongation of 
the cilia. By means of these „Neuro- 
fibrillen” the cells seemed to be connected 
with other nerve cells lying behind the differentiated epithelium. 
However I could not until now state that with a sufficient amount 
of certainty. 
On cross-sections the differentiated part of the floor appeared as 
