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other sort (smelling-cells) have an anterior portion much 
narrower than the nucleus, and an excessively fine long 
thread-like prolongation from the deeper surface, which 
passes towards the connective tissue layer Exner, however, 
cannot confirm Max Schultze as to the essential differences 
between these two forms, and is, accordingly, not prepared to 
assign them distinct functions, as that histologist has done. 
He denies that the nuclei differ in the two forms, but finds 
that the nucleus exhibits some variation in form and optical 
character in both. He also states that the difference in the 
thickness of the portion of the cell in front of the nucleus is 
of no importance, since he has most carefully and amply 
observed forms of intermediate thickness. Pigment-drops 
also occur in the thin anterior piece of the smelling-cells, 
as well as in the broad epithelial-cells. Schultze pointed out 
a difference between the two kinds of cells in the presence of 
hair-like projections on the ‘smelling-cells.” But Exner 
finds these on the epithelial-cells too. He attributes the 
absence of them, which is commonly remarked, to their 
getting detached; such portions of epithelial-cells, e.g. in 
the case of the striated piece on the cells of the intestinal 
villi, not unfrequently becoming broken away under the 
influence of reagents. 
Exner says he has been very careful not to confuse the 
proper epithelial-cells of the olfactory region with the ciliated 
epithelium of the surrounding parts, and gives drawings of 
two or three undeniable cases in support of his state- 
ment, the best of which were obtained by the osmic acid 
method. That there should be two forms of cells which 
equally have claims to be regarded as “ smelling-cells” is of 
interest, in conjunction with the fact that two forms of 
nerve-endings, the rods and the cones, occur in the eye. It 
would be worth inquiring whether any transition forms 
between rods and cones occur in the retina as here, between 
“ epithelial-” and ‘‘ smelling’’-cells, and whether, in either 
case, the transitional forms indicate an actual metamorphosis 
of the one form into the other—points of which Dr. Exner 
does not profess to treat. ‘The parallel is striking between 
the very delicate “ centrale Forssatz’’ of the “ smelling-cells”’ 
and the similarly delicate thread coming from the “ rods,” 
on the one hand, and the thicker corresponding parts of both 
so-called epithelial cells and the cones. 
The subepithelial network is a nervous structure, which has 
been more or less clearly seen by previous observers, and 
which is very exactly represented in the tongue of the frog, 
as described both by Axel Key, and more recently by Engel- 
