NOTES ON A TRACT OF MODIFIED ECTODERM. 101 
tissue, in which the modified portion rests (PI. III., figs. 1, 
2, 3, x.,z.z.); the epithelium is not only much deeper, but 
the epithelial cells may be seen frequently to end below 
in long colourless tails or threads, which are in connection 
with a mass of tissue lying below them, and on the outside 
of the sub-epithelial tissue. This mass consists of stellate 
cells (Pl. IV., fig. 5, and Pl. V., figs. 1—4); the nucleus 
and nucleolus stain deeply with picro-carmine, but the 
outer part of the cell is colourless and hyaline; the points 
of the stars are produced into long colourless threads 
connected in some cases with the threads from the outer 
columnar cells ; many appear to be lost in the section, 7.e. 
they pass out of the plane of the section, and some leave 
_the epithelium in a group, and enter the sub-epithelial 
tissue as a bundle of fibres (Pl. FV., fig. 5, and Pl. V., 
figs. 1, 2 and 4). The bundles sometimes pass for some 
distance through the epithelium before leaving it (Pl. V., 
fig. 4); they appear to enter the sub-epithelium only 
where the channels are deepest. The channel on the 
outer aspect of the fold is deeper than the one on the 
inner side. These fibres certainly pass through the sub- 
epithelial tissue from one to the other of the two areas 
of modified tissue on the opposite sides of the fold, and 
also to the empty canal, which they may be seen to enter 
(Pl. III., fig. 3), and although I cannot trace them con- 
tinuously, solitary fibres, I believe, pass through this 
bundle to the deep epithelium at the base of the tentacles. 
The modified epithelium on the outer aspect of the fold 
extends apparently from the apex of each arm to its base, 
but it does not quite reach to the region of the mouth on 
either side; the normal columnar epithelium gradually 
taking the place of the modified portion. ‘The modified 
epithelium, between the fold and the tentacles, is only 
observable in the free portion of the arms, and cannot be 
